Resettable fuse - packaging process

Resettable fuse - packaging process(Metal Oxide Varistor)

Select modified epoxy resin polyethylene / carbon black self-recovery fuse packaging materials, and to study the impact of the package on the thermal characteristics of the fuse, the encapsulation layer affect the heat capacity of the core material, through current is large enough, the package fuse action time almost no effect, and when the through current is smaller, the encapsulation layer at 120 ° C (melting point of polyethylene) curing the fuse a certain gap exists between the encapsulation layer and the core material, the deterioration of cooling capacity of the core material, and the thermal expansion of the core material can be carried out smoothly, shorter operating time. Therefore, fuse encapsulated in the core material should reach a temperature of the maximum thermal expansion.

Resettable fuse - related issues

What fuse is it?

The fuse is also known as fuse, IEC127 standards will define it as "fuse (fuse-link). It is a mounting electrical components in the circuit, to ensure the safe operation of the circuit. The role of the fuse: circuit failure or abnormal, accompanied by rising current, and elevated current may damage some important devices in the circuit or expensive devices, and may even cause a fire burned circuit. Circuit correctly placed fuse, then the fuse will be in the current abnormally elevated to a certain height and a certain amount of time, their own fuse to cut off the current, which play the role of the safe operation of the protection circuit. Earliest fuse in Edison invented more than a century ago, is very precious, so initially it is used to protect expensive incandescent industrial technology developed incandescent.

The works fuse is what? (Metal Oxide Varistor)

All know, when the current flowing through the conductor, the conductor exists a certain resistance, the conductors will heat. And heat follow this formula: Q = 0.24I2RT; wherein Q is the amount of heat, and 0.24 is a constant, I is flowing through the conductor current, R is the resistance of the conductor, T is the current flowing through the conductor; so formula is not difficult to see a simple fuse works.

When the production of the fuse material and its shape is determined, the resistor R is determined relative to its temperature coefficient of resistance (if no consideration). When current flows through it, it will heat, its heat is also increasing with increasing time. The current and the size of the resistor determines the speed of generating heat, the fuse structure and its installation conditions to determine the rate of heat dissipation, and if the velocity is less than the speed of heat dissipation generated heat when the fuse is not blown. If the speed of heat is generated is equal to the speed of heat dissipation within quite a long time, it does not fuse. Produce heat speeds greater than the speed of heat dissipation, the heat generated will be more and more. Because it has a certain specific heat and mass, the increase in heat in the temperature rise on the fuse occurs when the temperature is raised to above the melting point of the fuse of the fuse. This is the fuse works. They should know from this principle in the design and manufacture of fuse must carefully study the physical characteristics of your chosen material, and to ensure that they are consistent geometry. Because of these factors on the fuse normal work since an important role. Similarly, when you use it, be sure to properly install it.

Fuse structure? What are the functions of each? What is required?

General fuse is composed of three parts: First, melt part, it is the core of the fuse, the blown play off the current role, the same class, the same specification fuse melts, the material has to be the same, the same geometric dimensions, the resistance value as small as possible and to be consistent, it is the most important is the fusing characteristics to be consistent; second electrode portion, there are usually two, which is the important member of the melt and a circuit coupled, it must have good electrical conductivity, should not produce significant the installation of contact resistance; bracket portion, a melt of the fuse are generally slender and soft, and the role of the stent is to melt fixed and three parts become rigid overall ease of installation, use, it must have good mechanical strength, insulating properties, heat resistance and flame retardancy, in use, should not produce fracture, deformation, phenomena such as combustion and short;

The fuse power circuits and high-power devices used, not only general fuse three parts, but also interrupter device, because of the type of fuse protection circuit is not only the work of current and when the melt blown two terminal voltage is also high, often melt has melted (fused) or even vaporized, but the current is not cut off, and the reason is that in fusing the moment in the role of the voltage and current, the fuse between the two electrodes pull arc phenomena. This interrupter device must have a strong insulation and good thermal conductivity, and is negatively charged. Quartz sand is the commonly used the interrupter material.

In addition, there are some fuse indication device, and its role is when the action fuse (fuse) after the occurrence of certain changes in appearance, easy maintenance staff found, for example: luminous, color, pop-up solid indicator. (Metal Oxide Varistor)

Resettable fuse - parameters

Resettable fuse - parameters(Metal Oxide Varistor)

IH: Maximum operating current (25 ℃)

IT: Minimum operating current (25 ℃)

Itrip: overload current

Tmax: maximum overload current action time

Vmax: maximum overload voltage

Imax: maximum overload current

Rmin: minimum resistance (25 ℃)

Rmax: maximum resistance (25 ℃)

Resettable fuse - Application

Since the resumption of the the fuse series DIP DIP or SMD surface mount DC / AC power supply circuit. PPTC polarity of points. PPTC in the protection of the state, the surface temperature is high, to be installed in the ventilation status under high-temperature-sensitive components not in direct contact with the PPTC.

Applications:

ADSL equipment in the self-recovery fuse applications

Self-recovery fuse in the radio product, battery pack and charger products automotive electronics and auto parts overcurrent protection applications

Remote control electric toy car, high-low-frequency power charger electric toys, stroller and other electronic toys

Application of products in the satellite receiver DVB

Resettable fuse in the communication terminal equipment products

Power supply products

Home theater / speaker / crossover / electromagnetic load / motor / vacuum cleaner

Self-recovery fuse applications:

Ballast

Fluorescent lamps require a ballast to generate a high voltage and high current to point. The electrical characteristics of the ballast control fluorescent lamps. Produce high impact both ends of the electronic ballast of the lamp lights when the lamp lit, to form a self-oscillation circuit in the electronic ballast, the control of the oscillation circuit by the transistor. Many electronic ballast is due to lamp failure. Lamp shorted to achieve use deadline or lights are taken to open an overcurrent condition, and lead to the cathode of the lamp open. Due to the sake of the power factor, the load resistance becomes low. During starting, the ballast is in the non-normal operating current, high oscillation frequency state where more than three; switch circuit overcurrent and result in ballast failure.

Resettable fuse provide protection and fault protection transistor lights in the period of use is reached. Ballast failure often because the upper and lower terminal voltage of the transistor switch is open simultaneously, so the transistor fault protection is of great significance.

First, since the number of resettable fuse with automatic recovery performance, reduce rework and service, thereby reducing costs. Secondly, because resettable fuse can operate in extreme time, in order to protect some of the more sensitive resistor circuits, the ballast reliability and service life can be improved. Third, since the resettable fuse the power consumption is very low, does not appear the phenomenon of extreme heat and energy consumption in the the normal current working state. The resistance in the normal operating current is very small (usually only a few tenths of Ohms) and thus will not form an oscillation circuit. Fourth, self-resettable fuse small size, the space occupied by the circuit board, easy to design.

2 transformer(Metal Oxide Varistor)

With the failure of the power supply transformer is generated due to the over-current, resulting stream usually due to a short circuit or load decreases; cause failure circuit smoke, fire, and that damage to the circuit as well as interfaces. The low halide lamps light body structure transformer is often due to a short circuit fault. If improper installation and connection between the transformer and the lamp body, makes it easier to damage. Lamps are used in parallel, the short-circuit current. Installed resettable fuse to prevent short circuit and overload fault on the second coil of the transformer.

3 speakers

More stringent requirements on the protection of the speaker system. The ordinary fuse the speaker only from the disposable protective effect, so the increase in product failure rates; additional fuse box and wire manufacturer's costs increase. Also, the fuse must also meet the specifications, the error specifications fuse makes speaker damage. Install circuit breaker is a solution; However, they have not disconnected before off making noise. So, the best option is resettable fuse resettable fuse element. Self-resettable fuse in disconnected state (high-impedance state) is equivalent to a soft-switch will automatically revert to the failure to eliminate the state of the low resistance path.

4 Battery

a mobile phone battery pack: mobile phone battery pack key lies in its application characteristics, this battery is housed in a small and light and very narrow box inside. (NICD, NiMH, Li-ION) three major chemical batteries are installed in this universal inside the box. Now commonly used in a battery pack voltage is less than 10V, the maximum charging voltage of 16V, the latest varieties of the battery pack voltage is even lower, at between 3 ~ 4V. This means that the battery pack packaging changes very fast, from the development of the welding strip to the printed circuit board mount components. The battery packs are required circuit protection devices, such as VTP210G, able to 60C when the current maintained at about 1 amps. Protection circuit resistance is lower, the smaller the energy consumption, the greater the space of component selection.

b, cordless phone batteries: the cordless telephone via the current and voltage is relatively small. SRP120, LTP070 and LTP100 are good overcurrent protection devices.

c, radio communication battery: radio communication with current mobile phone battery current, than small laptop operating current. LR4 series of working current of 7.3 amperes, small size, light weight, and is very suitable for this application. With large current SRP or LTP series can also be applied.(Metal Oxide Varistor)

B) chemical batteries

Increasingly wide application of chemical batteries, the application of these components will cause the battery pack to have a better, lower-cost protection device.

A, NiCD battery: low impedance, stable chemical characteristics NiCD battery not like NiMH and Li-ION battery, as on so sensitive overcurrent. However, due to the low loss, the application is still very widely. However, in the short-circuited or overcurrent state, the low internal resistance will lead to a higher current through. The reasons for the failure of these batteries are usually over-current, instead of overheating, the products are suitable for application by any battery material.

B, NiMH battery: NiMH batteries have a higher energy density than NiCD battery. When more than 90C, these batteries are more easily degraded. Use the VTP or the LTP than SRP/LR4 material more suitable for the protection of this type of battery. According to the design method of the battery, SRP and LR4 can the battery protection, but using the LTP thermal performance when the VTP is stronger.

C, Li-ION battery: all chemical batteries, the energy density of Li-ION battery, the chemical properties of the most sensitive. , Need to be equipped with a circuit protection device in use and when charging. Now commonly used protective device is an integrated circuit, but this is not the most secure, because of the integrated circuit itself, may also cause a short circuit or a CMOS startup failure of the protective device unsafe. When more than 90C, Li-ION battery also began to degenerate, this battery voltage, circuit protection requirements even more stringent. LTP, SRP series as early as the battery, but the most appropriate PTC element VTP; the LR4 series of action shorter time for large capacity Li-ION battery, more than SRP series.

1, resettable fuse rechargeable battery pack

1), the problem with the analysis: NICD, NiMH, Li-ION special protection circuits commonly used in mobile phones and computers. Usually due to failure of these battery packs: the positive and negative terminals accidental short circuit; charger can not stop charging the battery fully charged; hold against the wrong charger or battery polarity. PTC SMD series installed in series in each cell of the battery pack to provide over-current and over-temperature protection circuit.

2), and protection requirements: when a failure occurs, the mobile phone of the voltage up to 16V, the voltage of the computer can achieve 24V; its current can be up to 100 amperes. In overcharge condition, the battery pack needs to be over-temperature protection, the the NiCD battery can not exceed 120C, NiMH and Li-ION battery can not exceed 90C.

3), the PTC element selection: LTP, VTP and LR4 commonly used in mobile phones and cordless phones, has higher holding current of the SRP, LTP and LR4 series commonly used in desktop and laptop computers. NiMH battery pack, VTP LTP material allows designers to increase the protective function of the thermal conductivity. Some special application of the patch and VTP Series the AAA battery unit can be used.(Metal Oxide Varistor)

Resettable fuse - species

Applications(Metal Oxide Varistor):

Through the protective device RF/WH600 series of products designed for the design and production of program-controlled switches, patch panels, transformers, security equipment, lamps, ballasts, meters, telephone lines and other fields can also be used to.

Applications: RF/WH250 products designed for program-controlled switches, patch panels designed production through the protective device can also be used for the transformer, security equipment, lamps, ballasts, meters, telephone lines and other areas.

Applications:

The RF/WH120 series of products is designed and manufactured specifically for ballast overcurrent protection devices.

Applications:

RF/WH60, RF72 products are widely applied to the higher rated working voltage circuit, such as micro-motors, speakers, transformers, security equipment, industrial control, test and measurement equipment, satellite receiving systems, the toy industry and other fields.

Applications:

RF/WH30 series products are widely applicable to medium-circuit withstand voltage capability, such as micro-motors, computer interface, the mouse, the CPU, transformers, security equipment, test and measurement equipment, satellite receiving systems, the toy industry and other fields.

Application the range: RF/WH16 products suitable for low operating voltage, operating current circuit, can be widely used in the field of power converters, motorcycles, cars, computer power supplies, micro-motors, computer interface, CPU, etc..

Applications:

The RF/WH6 series of products for the lower operating voltage, operating current is relatively small circuit, such as computers, computer peripherals, and the toy industry and other fields.

Surface Mount SMD resettable fuse range of applications:

SMD chip self-recovery fuse: SMD self-recovery fuse products designed for program-controlled switches, patch panels, design and production of over-protection devices, transformers, security equipment, lighting, automotive electronics, industrial control, communications, instrumentation, telephone lines can also be used to and other fields.

SMD resettable fuse characteristics

1. Meet RoHS requirements

2.EIA Size: 0805 to 2920

3. Maintain current range: 0.05 ~ 3.0A

Voltage level from 6V to 60V, to meet the computer and a variety of electronic applications require

5. Pad size small

Fast time.

7. Impedance low

8 operating voltage range: -40 to +85 ° C

Safety Certification: UL / cUL / TUV

10. Variety, full specifications, alternatives of Raychem, LITTLEFUSE, BOURNS, AEM, Po Dentsu such as imports Model

11 small size, rugged construction, easy automated installation

SMD resettable fuse range of applications

Computers and peripherals.

Mobile phone battery pack

3. Automotive electronics

4 Power Supply

5. Communication system

6 Other Applications

(Metal Oxide Varistor)

The overcurrent sheet Overview: overcurrent protection sheet is designed to prevent the battery over-temperature caused by the charge due to overcharging, the battery over-temperature is a major concern of the battery pack design personnel. Lithium battery group overvoltage and overcurrent detection security protection circuit (including integrated circuits and semiconductor circuit as in the case of strong electrostatic discharge, temperature and short circuit failure.) But voltage protection circuit failure without temperature protection, the battery will overcharge or abuse charge generated too much heat, the battery rupture, leakage, smoke, or even burning.

Huaju Gong Division launched a new strip overcurrent protection piece, the resistance is low compared with previous products, the device can also play over-current protection and over-temperature protection, designed to meet the longer working hours in order to reduce the impedance of the battery pack, The requirements of the portable electronic product designs. Particularly suitable for the lithium ions and nickel-hydrogen is more sensitive to the temperature of the secondary (rechargeable) battery.

Battery over-current protection chip and battery pack inside the original battery in series, regardless of the temperature rise is caused by a short circuit caused by the overcharge, the device can play a protective role, no thermal fuse or bimetal circuit breaker. This entry like devices using nickel pin, small size and thin, can be welded directly to the original battery, save space and reduce installation costs

WMZ12A type PTC thermistor is mainly used [transformer (adapter) / primary coil / charger / digital multimeter / intelligent power meter / micro motor / transistor], overcurrent overheat protection, directly in series with the load circuit, in the line abnormal situation, it is able to automatically limit current or blocking current, and then restore the original state, commonly known as the "fuse" when troubleshooting.

Features:

Non-contact circuits and components overcurrent protection automatically limits

Automatically return to work after troubleshooting no noise no spark

Reliable, easy to use

3. Applications principle:

The WMZ12A type PTC thermistor in series in the power supply circuit, when the circuit is in the normal state flow through the PTC current less than rated current, PTC is in the normal state resistance is small, does not affect the electronic ballast (energy-saving lamps, transformer, multimeter) protection circuit work properly. When the circuit current is greater than the rated current, PTC suddenly fever, resistance surge up to the high-impedance state, thus limiting or blocking current protection circuit from damage. Current current back to normal, PTC also automatically revert to the low resistance state, the circuit to resume normal work.

The WMZ12A type PTC thermistors overcurrent protection applications in electronic ballasts (energy-saving lamps, transformer, multimeter), Nanjing, China giant advantage by virtue of its scientific research and technology and other aspects of the first to introduce a high withstand voltage (V ≥ 300VAC The) featuring WMZ12 products.(Metal Oxide Varistor)

Resettable fuse

Resettable fuse(Metal Oxide Varistor) is a high-tech polymer resin and nano conductive grain is made with a special processing, under normal circumstances, the nano conductive crystals form a chain with the resin matrix link conductive pathways, fuse normal work; circuit short circuit or overload its large current flowing through the fuse set temperature rise, when the Curie temperature is reached, the state density decreases rapidly, the phase change is increased, the internal conductive link was the avalanche state variable or rupture, fuses was step type relocated to the high-impedance state, the current rapid clip off fast, accurate circuit limit and protection, its tiny current fuse has been in a protected state when power outages and troubleshooting, the set temperature decreases, the density of states increase large phase change recovery, nanocrystals reduced into chain-like conductive paths, and self-recovery fuse restore to the normal state, without artificial replacement.

An operation principle of the self-recovery fuse is an energy homeostasis, the current flowing through the RF / WH series component heat is generated due to the RF / WH series relationship, the heat generated in whole or in part, for distributing to the environment, but not dissipate heat would raise the temperature of the components of the RF / WH series.

Work properly when the temperature is low, the heat generated and the heat dissipated to reach equilibrium. RF / WH series element in the low resistance state, the RF / WH series does action, when the flow through the components of the current of the RF / WH series increases or the ambient temperature increases, but if it reaches a balance of the heat generated and the heat dissipated, the RF / WH series is still not action. When the current or the environmental temperature is further increased, the RF / WH Series will reach a higher temperature. If the current or the ambient temperature continues to increase, the heat generated may be greater than the heat dissipated, so that the RF / WH series element temperature surge, at this stage, a small temperature change will cause a substantial increase of the resistance, which When RF / the WH series elements in a high-impedance protection status, limits the current by an increase in impedance, the current in a very short period of time a sharp decline, thereby protecting the circuit apparatus from being damaged, as long as the voltage applied to the heat generated is sufficient RF / WH series component emit heat in the RF / WH Series components change state action has been in the state (high impedance). When the applied voltage disappears, RF / WH series can be automatically restored.

Resettable fuse - technical standards

1, Rated zero power resistance

The PPTC thermistor should be zero-power resistance profile packaging, and resistance range marked on the package. Pressure, after the test of the resistance to flow capacity, each sample itself before the resistance change rate Terrible δ is | before Ri after-Ri / Ri ago - (RJ after-Rj) / Rj before | ≤ 100%

2, PTC effect

That a material having a PTC (Positive Temperature Coefficient) the effect, i.e. the effect of the positive temperature coefficient, and refers only to the resistance of the material will increase with increasing temperature. As most of the metal material with PTC effect. In these materials, the PTC effect manifests resistance with temperature increases linearly, which is usually said linear PTC effect.

3, non-linear PTC effect

The phase change material will exhibit a phenomenon that the resistivity along the narrow temperature range of the sharp increase in several orders of magnitude of a few ten nonlinear PTC effect. The considerable variety of types of conductive polymer experience showing this effect, such as the polymer PTC thermistor. These conductive polymer for an overcurrent protection apparatus for manufacturing very useful.

4, the initial resistance Rmin(Metal Oxide Varistor)

Before being mounted to the circuit, under the conditions of an ambient temperature of 25 ° C test, the resistance of the polymer PTC thermistor of the RF / WH series.

5, Rmax

At room temperature, RF / WH series of polymer PTC thermistor action or reflow soldering installed the maximum resistance value measured one hour after the circuit board.

6, minimum resistance (Rmin) / maximum resistance (Rmax)

In the specified ambient temperature, for example: 25 ℃, prior to mounting to the circuit the particular model RF / WH series polymer thermistor of the resistance will within a predetermined range, i.e. in the minimum value (Rmin) and the maximum value (Rmax ) between. This value is listed in the resistance of the specifications book column.

7, to maintain the current Ihold

Maintain current is the maximum current that can be adopted in the case of RF / WH series of polymer PTC thermistor maintain no action. Under defined environmental conditions, the device can maintain the indefinite length of time, and will not be changed from the low resistance state to the high impedance state.

8, the operating current Itrip

Under defined environmental conditions, so that the RF / WH series of polymer thermistor smallest steady state current in the operation within the time limit.

9, the maximum current Imax (resistance to flow value)

State limit, RF / WH series of polymer PTC thermistor safety action maximum operating current, the thermistor resistance to flow values. Exceeds this value, the thermistor may damage, can not be restored. This value is listed in the resistance to flow of the specifications book value of a column.

10, the leakage current Ires

RF / WH Series Polymer PTC thermistor is locked in its high-impedance state when the current through the thermistor.

11, the maximum operating current / normal operating current

Under normal operating conditions, the maximum current flowing through the circuit. Maximum ambient operating temperature of the circuit used to protect circuits RF / WH series of polymer PTC thermistor maintain current general than the operating current.

12, Action

RF / WH series of polymer PTC thermistor in the process of the current increase in ambient temperature change from low resistance to high resistance.

Parameters of the standard

13, the action time

Over-current occurs and the time required for start to the completion of the thermistor action. Any specific RF / WH series of polymer PTC thermistor, the greater the current flowing through the circuit, or the higher the temperature of the work environment, the shorter the time of the action.

14, Vmax maximum voltage (pressure value)

RF / WH Series polymer PTC thermistor action under limited conditions, can safely withstand the highest voltage. Thermistor voltage value. Exceeds this value, the thermistor may be breakdown can not be restored. This value is usually listed in a column of the withstand voltage of the specifications book.

15, the maximum operating voltage

In the normal operating state, the maximum voltage across the RF / WH series of polymer PTC thermistor at both ends. In many circuits, the equivalent circuit of the power supply voltage.

16, the conductive polymer

This means by the conductive particles (carbon black, carbon fiber, metal powder, metal oxides, etc.) are filled with an insulating polymer materials (polyolefins, epoxy resins, etc.) and the obtained conductive composite material.

17, ambient temperature,

In the temperature of the thermistor or an associated circuit of the thermistor element surrounding stationary air.

18, the working temperature range

P components can safely work environment temperature range.

19, the maximum operating ambient temperature

The expected element can safely work the maximum ambient temperature.

20, the power loss(Metal Oxide Varistor)

The power consumed by the RF / WH series of polymer PTC thermistor action, by calculating the flow through the thermal resistance of the leakage current and to obtain the product of the voltage across the thermistor.

21, high-temperature, high-humidity aging

RF / WH series of polymer PTC thermistor in a long time (e.g., 150 hours) is measured at room temperature, before and after the changes in resistance at higher temperatures (eg 85 ℃) and high humidity (85% humidity) Status.

22, passive aging test

Room temperature, the measurement of the RF / WH series of polymer PTC thermistor for a long time (1000 hours) in the state before and after the change in resistance of the higher temperature (such as 70 ℃ or 85 ℃).

23, hot and cold blow test

At room temperature, RF / WH series of polymer PTC thermistor resistance changes before and after temperature cycling test results. (For example, the 10 cycles between -55 ° C and +125 ℃).

24 PTC strength β

PTC thermistor has adequate PTC intensity the NTC phenomenon and can not be. β = lgR140 ° C / R ≥ 5 R140 ° C at room temperature and the R room temperature to 140 ℃ with the rated zero-power resistance value at room temperature.

25, the operating characteristics

PTC thermistor the pressure resistance flow test before and after should not operating characteristics test, and, where R is a non-operating characteristic test the thermistor at both ends of the U / I, Rn is rated zero-power resistance preliminary tests value or retest values.

26, the recovery time

The PTC thermistor action after the recovery time should not be greater than 60S.

27, failure mode test

During failure mode test, the the high poly PTC thermistor may be supplied with the test or in a failed state, allow the failure mode is open or high impedance state, but not low resistance state or from the open flame during the entire experiment.(Metal Oxide Varistor)

Film Capacitors ll

Film capacitors(Metal Oxide Varistor), film capacitor is widely used in the cross-linking of the analog signal, power supply noise bypass (anti-cross-linked) place. The film capacitor When the electrode based on a metal foil, and polyethylene ethyl acrylate, polypropylene, poly stupid plastic film such as vinyl or a polycarbonate, from the overlap of the ends, wound into a cylindrical structure of a capacitor.

    Nickname film capacitors

        Capacitor categories, called on their models in the market are not uniform:

        1, polyester capacitors: usually say polyester capacitors Model: called for PEI in adapting the CL11 to foreign countries or foreign companies or PEM, the main material for polyester film, the full name of the felt-type polyester / ester film capacitors, the price of such a capacitor cheap, small size, electrical performance is not bad, the loss slightly bigger.

        2, metallized capacitor: the domestic call CL21, CBB21 (a lot of people capacitor CBB model called CBB capacitor), foreign called MEF and MPP Its main material is polyester metallized film and polypropylene metallized film(Metal Oxide Varistor).

        3, CBB capacitor: CBB21, CBB18, CBB81 capacitor collectively, people say CBB capacitor means CBB81 abroad called the PPS metallized polypropylene capacitors within the string type high-pressure, anti-current voltage capability, loss is the safest choice of most engineers, the drawback is that expensive, bulky, feet away from the general in 15,20 mm.

        4, polyester capacitors and polypropylene capacitors: called raw materials for capacitors, CL is a polyester material, CBB polypropylene material.

    The thin film capacitor structure

        The internal structure of the thin film capacitor main ways: metal foil (or on plastic foil obtained by metal processing) as an electrode plate, to the plastic as the dielectric. Through winding or multilayer technology derived. The various arrangements of the foil and the film can be derived from a variety of configurations.

    The classification of the film capacitor

        1, the dielectric classification;

        (The medium electrode plate) arrangement taxonomy;

        3, the structure of the taxonomy;

        The line ends taxonomy.

    The classification of a film capacitor

        Depending on the dielectric film capacitors can be divided into the following three categories:

        A, T type: i.e. PE T-Polyethylene terephthalate (polyethylene terephthalate (or ester))

        , P-type: P P-Polyethylene (polypropylene)

        3, N-type: i.e. PE N-Polyethylene naphthalate (polyethylene naphtha)

    The main characteristics of the thin film capacitor

        Film capacitors on the application of the main characteristics:

        1, Promise sexual;

        Insulation resistance is high;

        3, excellent frequency characteristics (wide frequency response);

        4, the dielectric loss is small.

    Function of the film capacitor

        DC power supply lines is mainly applied to the DC voltage control apparatus(Metal Oxide Varistor) commercial frequency ripple less, while avoiding transmitted to the AC power line control means generates high-frequency clutter, so looking into the capacitor from the AC power line or rectifier, For 50Hz frequency, it is necessary to render the low impedance; looking into the capacitor by the control device for high-frequency clutter, but also presents a low impedance; if impedance is 0, then the ripple voltage and high-frequency clutter voltage will become 0.

        Therefore, the electrode area S is increased, the electrical capacity can be increased. In addition to the electric capacity, often also parasitic various impedance, in the occasion of the electrolytic capacitor, the electrode is configured to elongate metal foil wound into a cylindrical shape, in addition to the electric capacity, yet additional elongate electrodes arising inductance component. Further, the electrode leads to an external terminal used wire inductance component; while the ratio of the electrolyte constituting the electrolytic capacitor of the cathode resistance of about 100 Ω-cm, and this is one of the elements to restrict the effect of the filtering.

        The capacitor of the film (film) based on the plastic film as an insulating material, the metal foil wound into a cylindrical shape or become integrated layered, in order to increase the area. However, in the occasion of the film capacitor into a cylindrical shape, even if the wound, since the electrode leads to pass through the metal flame spraying for the contact (metalcon) a after its inductance can be reduced a lot.

        The efficacy of the film capacitor in parallel

        A transistor down chopper (chopper), the 50kHz as switching DC power line high-frequency clutter voltage waveform. 2200μF electrolytic capacitor terminal, about there 2V of the clutter, if 2.2μF film capacitor in parallel, it will inhibit become 0.1V. If the electrical capacity of the thin film capacitor is not sufficient, the peak voltage of the clutter will be reduced, the vibration frequency is low, it will easily be seen(Metal Oxide Varistor).

Film Capacitors

Film capacitor (Film Capacitor(Metal Oxide Varistor)) is also known as plastic film capacitor (Plastic Film Capacitor). To the plastic film as a dielectric.

Description:

The capacitor according to different media, many of its kind, for example: electrolytic capacitors, paper capacitors, film capacitors, ceramic capacitors, mica capacitors, air capacitance. But the most frequently used in audio equipment, undoubtedly electrolytic capacitors and film capacitors (Film). Most of the electrolytic capacitors are used in a lot of places that need power capacity, for example, the main power supply filter capacitor part, in addition to filtering, and also cater to store electrical energy. While the film capacitors are widely used in the bypass to the cross-connected, power supply noise of the analog signal (anti-cross-linked) and other places.

Structure and classification:

The film capacitor When the electrode based on a metal foil, and polyethylene ethyl acrylate, polypropylene, poly stupid plastic film such as vinyl or a polycarbonate, from the overlap of the ends, wound into a cylindrical structure of a capacitor. Accordance with the type of plastic film and are respectively known as poly ethyl capacitance (also known as Mylar capacitor), polypropylene (also known as PP capacitors), polystyrene capacitance the (called PS capacitor) and poly carbonate capacitance.

A typical schematic diagram on the film capacitor.

Features:

Film capacitors has many excellent features, it is an excellent performance of the capacitor. Reciprocity as follows: polarity, insulation resistance is high, excellent frequency characteristics (wide frequency response), and the dielectric loss is very small. Based on the above advantages, the thin film capacitor is large-scale use in the analog circuitry. Especially in the part of the signal cross-connection, you must use good frequency characteristics, low dielectric loss capacitor in order to ensure that the signal transmission, without too much distortion occurs.

Its structure and the same paper dielectric capacitors, the medium is such as polyester or polystyrene. Polyester film capacitors, high dielectric constant, small size, large capacity, better stability, suitable as a bypass capacitor. Polystyrene film capacitors, dielectric loss, high insulation resistance, temperature coefficient, can be used for high-frequency circuits.

Among all of the plastic film capacitor, the capacitance characteristics of polypropylene (PP) capacitor and polystyrene (PS) is most significant, of course, both the price of the capacitor is also relatively high. Audio equipment in recent years, however, in order to enhance the sound quality of the parts and materials used has become more and more advanced, the price is not the most important factor, so in recent years, PP capacitors and PS capacitors are used in the frequency and quantity of audio equipment Yulai higher. Readers can often see a certain brand of equipment, known how much a certain brand-name PP quality capacitor or PS quality capacitors, as the sound quality endorsement truth in this.

Feature Summary: capacity range of film capacitors for 3pF-0.1uF, DC working voltage of 63-500V, suitable for high-frequency, low frequency, leakage resistance is greater than 10,000 Ω.

Edit this paragraph metalized film capacitors

Usually a thin film capacitor of its production method is wound together made of a metal such as aluminum foil as an electrode and a plastic film overlap. But another film capacitors and have a manufacturing method, called metallized film (Metallized Film), its production method is to vacuum deposition on a thin layer of metal on a plastic film as an electrode. So omit the foil thickness of the electrode, reduced the volume of the capacity of the capacitor unit, and so the film capacitor is more easily made compact, large capacity capacitor. Common MKP capacitors, metallized polypropylene film capacitors (Metailized Polypropylene Film Capacitor) on behalf of said MKT Metallized Polyester capacitor (Metailized Polyester) said on behalf of(Metal Oxide Varistor).

The metallized film capacitor using a film polyethylene ethyl acrylate, polypropylene, polycarbonate, etc., in addition to the wound-type, there are also stacked type. This type of metalized film capacitors has a so-called I recover the role (Self Healing Action), which assumes a tiny part of the fragile quality of electricity sector and cause a short circuit, caused by a short circuit around the electrode metal part of the electrode, or short-circuit current due to the electrostatic energy of the capacitor brought, and lead to the dissolution of the larger area integration evaporated to recover the insulation, the capacitor again returning to the role of the capacitor.

Metallized film capacitor features:

Metallized film capacitor that is in the surface of the polyester film of the vapor-deposited layer of metal film instead of the metal foil as the electrode, because the thickness of the metal film layer is much smaller than the thickness of the metal foil, so the wound volume than the metal foil capacitance is much smaller. The biggest advantage of metalized film capacitors is a "self-healing" features. The so-called self-healing properties is if the thin film dielectric because at some point in the presence of defects, and in the over-voltage under the action of a short-circuit breakdown, and the breakdown point metal layer may be in the arc under the action of an instant melting evaporated forming a small non-metallic area , the capacitance of the two pole pieces are re-insulated from each other and can continue to work, thus greatly improving the reliability of the work of the capacitor. Analysis principle, metalized film capacitors should not short-circuit failure mode, and metal foil capacitor there will be a lot of short-circuit failure phenomenon. Although the metal film capacitors great advantages as described above, but compared with the metal foil capacitor, there are the following two disadvantages:

First, the capacity stability than a foil type capacitor, which is due to the metallized capacitor in the long working conditions prone capacity loss and after healing may lead to reduced capacity, therefore, as an oscillation circuit with the capacity stability demanding. should be used in the metal foil capacitor better.

Another major drawback to withstand a large current capacity is poor, which is weaker a lot due to the metalized film layer to be thinner than the metal foils, the ability to carry large currents. To improve this shortcoming of the metallized film capacitors, metalized film capacitors in high-current products in the manufacturing process has been improved, the major improvements in ways 1) to do double-sided metallized film electrode; 2) increase the metallization layer thickness; 3) the end face of the metal welding process improvements to reduce the contact resistance.

  

Edit the market segment of the film capacitor application status(Metal Oxide Varistor)

Film capacitors used in electronics, household appliances, telecommunications, electric power, railway electrification, hybrid cars, wind power, solar power and other industries, the stable development of these industries, and promote the growth of the thin film capacitor market.

With the technical level of development, electronics, home appliances, communications and other industries replacement cycles are getting shorter, and thin-film capacitors with good electrical performance and high reliability electronic components promote these industries are upgrading an integral [1]. With digital, information technology, network construction further development and national increase in power grid construction, the electrified railway construction, energy-efficient lighting, hybrid cars and other inputs as well as consumer electronics products in the next few years to upgrade, film capacitor market demand further presents the trend of rapid growth.

According to the China Electronic Components Industry Association statistics, it is expected that in 2010, the global film capacitor market will be 15 to 20% of the speed of rapid growth, film capacitor market growth will drive the rapid growth of the market of polypropylene electronic film(Metal Oxide Varistor).

Safety capacitor

Safety capacitor(Metal Oxide Varistor) for such occasions, that the failure of the capacitor would not lead to electric shock, do not endanger the personal safety which includes the X capacitor and Y capacitors. x capacitance is connected across the capacitance between the two lines in the power line (LN), generally used in the metal thin film capacitor; The Y-capacitor is connected across the capacitance between the two lines and the ground of the power line (LE, NE), and generally occur in pairs . Based on the leakage current limit, the the Y capacitor value can not be too large, the general X capacitor uF level, Y capacitor is nF level. X capacitor differential mode interference suppression. The Y capacitor suppress common mode interference.

The safety capacitor security level

Permissible peak pulse voltage the safety capacitor security level applications overvoltage level (with the IEC664)

  

X1> 2.5kV ≤ 4.0kV Ⅲ

X2 ≤ 2.5kV Ⅱ

X3 ≤ 1.2kV -

A safety capacitor security level type of insulation rated voltage range

Y1 double insulation or reinforced insulation ≥ 250V

Y2 basic or supplementary insulation ≥ 150V ≤ 250V

Y3 basic or supplementary insulation ≥ 150V ≤ 250V

The Y4 basic or supplementary insulation <150V

The Y capacitor capacitance must be limited, so as to control the role of the rated frequency and rated voltage flowing through its leakage current size and the purpose of the system EMC performance. GJB151 provisions of the Y-capacitor should be no greater than 0.1uF. Y capacitor in addition to complying with the corresponding grid voltage withstand requirements of this capacitor in the electrical and mechanical properties sufficient safety margin to avoid short-circuit breakdown phenomena under extreme environmental conditions, Y capacitor voltage performance on protect the personal safety of great significance.(Metal Oxide Varistor)

Precautions

Capacitor for electromagnetic interference suppression

When the capacitor to eliminate noise in the power supply across the line circuit, not just the normal voltage, must also take into account the generation of abnormal pulse voltage (such as lightning), this capacitor may cause smoke or fire. So, across line capacitor safety standards for strict regulations in different countries, it must be used the safety certification capacitor.

Does not allow the DC capacitor used as a cross-line capacitor

For X2 electromagnetic interference suppression should be applied to not result in failure of the capacitor a shock hazard occasions, such as power cross-line connection, can withstand 2.5kV pulse voltage capacitor.

Y2 class electromagnetic interference suppression capacitor should be applied to the occasion of shock hazard, do not result in the failure of the capacitor for the power cross-line connection, can withstand 5kV pulse voltage shock, thus preventing the breakdown phenomena.

The safety capacitor IEC standard, advanced production technology and strict quality assurance system.

According to IEC 60384-14, the capacitor divided into X capacitors and Y capacitors the X capacitor capacitor cross the LN Y capacitor is a cross between the LG / NG capacitors. (L = Line, N = Neutral, G = Ground)

X capacitor bottom divided into X1, X2, X3, main difference is that: 1. X1 resistance to high pressure is greater than 2.5 kV, less than or equal to 4 kV the X2 high pressure resistance less than or equal to 2.5 kV, 3. X3 high pressure resistance less than equal to 1.2 kV

Y capacitor is divided into under the Y1, Y2, Y3, Y4, main difference is that: 1. Y1 8 kV high voltage is greater than 2. Y2 resistance to high pressure greater than 5 kV, 3 Y3 resistant high n / a 4 Y4 resistant high pressure greater than 2.5 kV

X, Y capacitor are safety capacitors, FireWire zero line between the X-capacitor, FireWire and ground Y capacitors are used in the power supply filter, play power filtering effect, respectively, of the common mode and differential mode interference from the filtering effect. safety capacitor for such occasions, that the failure of the capacitor will not lead to electric shock, do not endanger their personal safety. peak pulse voltage the safety capacitor security level application allows the over-voltage level (with the IEC664) X1> 2.5kV ≤ 4.0kV Ⅲ X2 ≤ 2.5kV Ⅱ X3 ≤ 1.2kV - the safety capacitor rated voltage range of the security level of insulation type Y1 double insulation or reinforced insulation ≥ 250V Y2 basic or supplementary insulation ≥ 150V ≤ 250V Y3 basic insulation or additional Insulation ≥ 150V ≤ 250V Y4 basic or supplementary insulation <150V Y capacitance of the capacitor must be restricted so as to control the effect of the rated frequency and rated voltage, flow through its leakage current size and performance of the system EMC purposes . GJB151 provisions of the Y-capacitor should be no greater than 0.1uF. Y capacitor in addition to complying with the corresponding grid voltage withstand requirements of this capacitor in the electrical and mechanical properties sufficient safety margin to avoid short-circuit breakdown phenomena under extreme environmental conditions, Y capacitor voltage performance on protect the personal safety significance

X capacitor filter circuit is jumper the LN-line; Y capacitor is NG line. The safety standards pulse voltage points X1, X2, X3 capacitance; insulation class points Y1, Y2, Y3 points. (None of these points is what material to learn more later.) As for the safety standards of various countries, there are some differences, but the rated voltage of no more than 250 and 400. The safety capacitor major manufacturers do is to meet the demand of the safety standards, a safety capacitor to meet the requirements of the Y capacitor, can be made to meet the requirements of the X capacitor. So there is the the safety capacitor superscript X1Y1, X1Y2 ...(Metal Oxide Varistor)

Indirect FireWire and 0 line capacitor is X, the FireWire and ground indirect capacitor like Y. Directly as FireWire and 0 line capacitance affected by the voltage peak to avoid the pressure rating of the short-circuit, pay more attention to the parameters, not set limits on the capacitance value. FireWire and direct ground capacitance leakage security problems related to its focus on the parameters insulation levels, as james bai said much capacitance values ​​will power outage on the devices of the people have an impact.

Safety certification

As security Y capacitor capacitance requirements must obtain a safety certification testing organizations. The Y capacitor appearance of orange or blue, are generally marked with a safety certification mark (such as UL, CSA logo) and pressure AC250V or AC275V words. However, the real DC withstand voltage up to 5000V. It must be emphasized that the Y-capacitor are not free to use the alternative nominal pressure AC250V or DC400V like ordinary capacitor.

2, also require safety testing organization must obtain certification as a security one X capacitor capacitance. X capacitors are generally marked with a safety certification mark and pressure AC250V or AC275V words, but its true DC withstand voltage up to 2000V nominal pressure AC250V or DC400V like ordinary capacitor to substitute when not free to use.

Breakdown problems

Cx capacitor filter if the breakdown, equivalent to the AC power grid short circuit, at least cause the device to stop working; capacitor Cy breakdown, equivalent to the AC grid voltage is applied to the casing of the device, a direct threat to the personal safety, and spread metal shell reference circuit or equipment safety, and often leads to some of the circuit or equipment burned.

Actual needs

X capacitor value according to actual needs, allowing larger than the Y-capacitor value, but must be a safety resistor in parallel at both ends of the X capacitor used to prevent When plugging or unplugging the power cord, the process of charging and discharging of the capacitor cause the power cord long charged. Prescribed safety standards when working into the machine power cord is unplugged, within two seconds, the charged voltage across the power cord (or ground potential) must be less than 30% of the original nominal operating voltage.(Metal Oxide Varistor)

How to choose a thermistor, should pay attention to what issues?

The type and model of the thermistor(Metal Oxide Varistor) more choose which one thermistor should be determined according to the specific requirements of the circuit.

Positive temperature coefficient thermistor (PTC) is generally used for refrigerator compressor starting circuit, color picture tube degaussing circuit, the motor overcurrent overheat protection circuit, current limiting circuit and thermostatic electric heating circuit. MZ-01 ~ MZ-04 series, MZ81 series, MZ91 series, MZ92 series and MZ93 series, such as commonly used in the thermistor has the starter circuit of the compressor. Can be selected according to the different types of compressor suitable for the thermistor it starts, start to achieve the best effect. Color television sets, computer monitors degaussing thermistor (Metal Oxide Varistor)  MZ71 ~ MZ75 series. According to TV, monitor the operating voltage (220V or 110V), current and degaussing coil specifications, the choice of the nominal resistance, the maximum starting current, maximum working voltage and other parameters are in line with the requirements of degaussing thermistor. Current limiting power thermistors PTC MZ2A ~ MZ2D series, MZ21 series, motor overheating protection MZ61 series PTC thermistor nominal resistance switching temperature, operating current and power dissipation parameters should be used to conform application circuit requires models.

Negative temperature coefficient thermistor (NTC) is generally used in a variety of electronic products for microwave power measurement, temperature detection, temperature compensation, temperature control and regulator with the appropriate type and model selection should be selected according to the needs of the application circuit . The common temperature detection series NTC thermistor MF53 and MF57 series, each series has a variety of models (the same type, different models of the NTC thermistor, standard resistance is not the same) to choose from. Common regulator with NTC thermistor MF21 series, RR827 series the thermistor voltage regulator can be selected based on the value of the reference voltage application circuit design values ​​and operating current. Temperature compensation, temperature control with NTC thermistor MF11 ~ MF17 series. Common temperature measurement and temperature control with NTC thermistor MF51 series, MF52, MF54 series, MF55 series, MF61 Department, the MF91 MF96 series, MF111 series, such as variety. MF52 series, MF111 series NTC thermistor is suitable for a temperature range of -80 ℃ ~ +200 ℃ temperature measurement and temperature control circuit. Series MF51, MF91-MF96 series NTC thermistor is suitable for temperature measurement and temperature control circuit 300 ℃. The MF54 series MF55 series NTC thermistor for temperature measurement and temperature control circuit in the 125 ° C or less. MF61 series MF92 series NTC thermistor applies to 300 ° C above the temperature measurement and temperature control circuit. NTC thermistor temperature control range meets the requirements of the application circuit, should pay attention to the chosen temperature control thermistor (Metal Oxide Varistor) .

ntc thermistor ll

NTC thermistor having a negative temperature coefficient thermistor(Metal Oxide Varistor). Is to use a single high-purity material, having a structure close to the theoretical density, high-performance ceramic. Therefore, in the miniaturization at the same time, also has a resistance value, small fluctuations in the temperature characteristics, and fast response to the detection of high sensitivity, high precision, can be a variety of temperature changes. The company provides a variety of shapes, features a small, high-reliability products, which can meet the application requirements of our customers.

B value of the NTC thermistor constant calculation

    The B value is a material constant of the thermistor, i.e. a thermistor chip (a semiconductor ceramic) is formed after high-temperature sintering, the material having a resistivity, for each formulation, and the sintering temperature is only a B value, So what kinds of material constants.

    B value thermistor material constant, or called thermal index.

    B value can be calculated through the measurement of the resistance value at 25 degrees Celsius and 50 degrees Celsius (85 degrees Celsius). B value, with the product temperature coefficient of resistance is a positive correlation, that is the larger the B value, the greater temperature coefficient of resistance.

    The temperature coefficient means the temperature is increased by 1 degree, the rate of change of the resistance value. B can be converted into a temperature coefficient of resistance value using the following formula:

    Temperature coefficient of resistance = B value / T ^ 2 (T want to convert a point of absolute temperature value)

    NTC thermistor B value is generally between 2000K-6000K, can not simply say the B value is the bigger the better or the smaller the better, it is up to you to use where. In general, as temperature measurement, temperature compensation, as well as the suppression the surge resistor with the product, under the same conditions, the B value big point. Because as the temperature changes, the resistance value of the B value of the products greater changes, that is more sensitive.

    These are made answer according to my own understanding, I do this, if you have any questions, you can add me as a friend, or send me a message.

    NTC thermistor B value is generally between 2000K-6000K, can not simply say the B value is the bigger the better or the smaller the better, it is up to you to use where. In general, as temperature measurement, temperature compensation, as well as the suppression the surge resistor with the product, under the same conditions, the B value big point. Because as the temperature changes, the resistance value of the B value of the products greater changes, that is more sensitive.(Metal Oxide Varistor)

    NTC thermistor B value formula: = the T1T2 Ln (RT1/RT2) / (T2-T1)

    Where B: B value of the NTC thermistor, provided by the manufacturers;

    RT1, RT2: thermistor in the temperature respectively when the resistance value of the T1, T2;

    T1, T2: absolute temperature scale. v

    NTC thermistor B value formula.

    To correct yesterday's post, I used precision thermistor 1 [%], not [%].

    B = T1T2 Ln (RT1/RT2) / (T2-T1) ---------- (1)

    B: NTC thermistor B value provided by the manufacturer;

    RT1, RT2: thermistor temperature for T1, T2 when the resistance value provided by the manufacturer the temperature is 298.15K (25 degrees C) resistance.

    T1, T2: absolute temperature scale.

    I was against the principles of yesterday Figure simple to talk about:

    By equation (1) can be obtained:

    B (1/T1-1/T2)

    RT1/RT2 = e -------------- (2)

    Take T1 = 298.15K, the resistance of the thermistor RT1 = 10K, so they chose R1 = 10K set temperature T2 when the sub-pressure value V2: V2 = RT2Vcc / (RT2 + R1) was RT2 = V2R1 / (Vcc-V2), so

    RT1/RT2 = Vcc/V2-1 into (2), we have

    B (1/T1-1/T2)

    e = Vcc/V2-1

    Have B (1/T1-1/T2) = Ln (Vcc/V2-1)

    T2 = T1 / (1-T1 (Ln (Vcc/V2-1)) / B)

    Set of 8-bit ADC output value of N Vcc/V2-1 = 256/N-1

    So T2 = T1 (1-T1 (Ln (256/N-1)) / B)

    Converted to Celsius

    T = T2-273.15

    You can compile a program in C or VB from N = 0 to N = 255 calculated thermometer, and N is the index look-up table directly to get the temperature. By actual test temperature values ​​constitute temperature form, using interpolation algorithms can also get a temperature value. I here T1 = 25 degrees, you can adjust the value of T1 to test a higher or lower temperature.

NTC thermistor resistance calculation

    Low-cost temperature measurement program NTC thermistor is used more, and generally use a look-up table method to obtain the temperature value, which involves correspondence between temperature and resistance. If you buy from the manufacturers NTC thermistor can be to the manufacturers temperature resistance table, but for ordinary lovers are thermistor buy from a retailer, selling components uncle and aunt will not provide you with resistance value and temperature control table. The usual method is standard thermometers, ambient temperature did not rise once measuring the resistance of the thermistor, the correspondence between resistance and temperature obtained by this method is more cumbersome, error is relatively large, poor control of other temperature changes; One way is calculated by the formula RT table, the temperature and resistance of the NTC thermistor temperature and resistance was not a linear relationship, but is calculated by the following equation can still correspondence relationship(Metal Oxide Varistor):

    Rt = R * EXP (B * (1/T1-1/T2))

    Of the above formula is explained as follows:

    1 RT is the resistance of the thermistor in the temperature T1;

    2. R is the nominal resistance of the thermistor T2 at room temperature;

    The B value is the important parameters of the thermistor;

    4. EXP is the n-th power of e;

    Where T1 and T2 refers to the the K degree that the Kelvin temperature, K = 273.15 (absolute temperature) + degrees Celsius;

    For example, I do a thermistor a MF58502F327 Model

    The MF58 - Model glass encapsulation

    502 - room temperature 25 degrees nominal resistance 5K

    F - allowable deviation of ± 1 [%]

    327 - B value 3270K NTC thermistor

    That it's R = 5000, T2 = 273.15 at +25, B = 3270, RT = 5000 * EXP (3270 * (1/T1-1 / (273.15 at +25))), this time substituting T1 temperature can be obtained the corresponding temperature thermistor resistance, pay attention to the temperature unit conversion, for example, we require 10 degrees Celsius above zero resistance, so T1 (273.15 +10).

    In order to facilitate the calculation we can take advantage of Excel's powerful formula to reduce the workload of manual calculations, if your software is very strong can write a small program to get.

    ----

    The choice of the size of the thermistor resistance

    Such as the measurement of the temperature of 10-100 degrees

    Voltage of 5,6 V with a 1000Ω the costs of electricity

    If voltage is about 1V, and then a large value, will certainly affect the accuracy.

NTC thermistor characteristic parameters of basic knowledge

    1.NTC negative temperature coefficient thermistor

    2.PTC positive temperature coefficient thermistor

    The physical characteristics of the thermistor is represented with the following parameters:

    Resistance value, the value of B, dissipation factor, thermal time constant, resistance temperature coefficient.

    Resistance values: R [Ω]

    Approximations of the value of the resistor is expressed as: R2 = R1exp [1/T2-1/T1]

    Wherein: R2: absolute temperature T2 [K] when the resistance [Ω]

    R1: the absolute temperature of T1 [K] when the resistance [Ω]

    B: B value [K]

    B value: B [k]

    The B value is a function of the resistance between the two temperature changes, the expression is:

    B = InR1-InR2 = 2.3026 (1ogR1-1ogR2)

    1/T1-1/T2 1/T1-1/T2

    Where: B: B value [K]

    R1: the absolute temperature of T1 [K] when the resistance [Ω]

    R2: the absolute temperature of T2 [K] when the resistance [Ω]

    Dissipation Factor: δ [mW / ° C]

    Dissipation factor is the ratio of electric power consumed by the objects and the corresponding temperature rise

    δ = W / T-Ta = I? R / T-Ta where:

    δ: dissipation coefficient δ [mW / ℃]

    W: thermistor electric power consumption [mW]

    T: reach thermal equilibrium temperature value [° C]

    Ta: room temperature [° C]

    I: at temperature T plus the thermistor value of current [mA]

    R: at the temperature T plus the thermistor on the current value [kΩ]

    Measuring temperature, you should pay attention to prevent the warming caused by the thermal resistance due to heating.

    Thermal time constant: τ [sec.]

    Thermistor under conditions of zero energy, the effect of the step so that the temperature of the thermistor itself changed

    Change, 63.2% of the time required to change between the initial and final values ​​when the temperature coefficient of thermal time τ.

    Resistance temperature coefficient: α [[%] / ℃]

    α shows the temperature of the thermistor changes every 1? C, the coefficient of the degree of change of the resistance value [i.e., the rate of change] with

    α = 1 / R? dR / dT, said calculation formula is:

    α = 1 / R? dR / dT × 100 =-B / T? × 100

    Wherein: α: Temperature coefficient of resistance [[%] / ° C]

    R: the resistance value of the absolute temperature T [K] [Ω]

    B: B value [K]

NTC thermistor detection method

    (A) measurement of nominal resistance value Rt

    With do not go directly to the contact with the thermistor or too close, to prevent damage to the thermistor.

    2, if the measured αt> 0, it indicates that the thermistor is not NTC but the FTC.(Metal Oxide Varistor)

Negative temperature coefficient thermistor

NTC negative temperature coefficient thermistor works(Metal Oxide Varistor)

NTC Negative Temperature Coefficient of abbreviations, the meaning of a negative temperature coefficient, refers to the negative temperature coefficient of semiconductor materials or components, the so-called NTC thermistor is a negative temperature coefficient thermistor device. It is based on metal oxides, such as manganese, cobalt, nickel and copper as a main material, and the ceramic manufacturing process made. These metal oxide materials have semiconductor properties, because the conductive way completely similar germanium, silicon and other semiconductor materials. The temperature is low, the number of these oxide material carriers (electron and hole) less, so its resistance value is high; as the temperature increases, the number of carriers increases, so the resistance value is lowered. The range of variation of the NTC thermistor at room temperature 10O ~ 1000000 ohms, the temperature coefficient of -2% to -6.5%. NTC thermistor NTC thermistors are widely used for temperature measurement, temperature control, temperature compensation.

NTC negative temperature coefficient thermistor(Metal Oxide Varistor)

NTC (Negative Temperature Coefficient) refers to the reduced resistivity exponential relationship, with a temperature rise phenomenon and material having a negative temperature coefficient thermistor. The material is sufficiently mixed with manganese, copper, silicon, cobalt, iron, nickel, zinc, and the like of two or more metal oxides, molding and sintering process is made of a semiconductor ceramic having a negative temperature coefficient, can be made (NTC) thermistor. Ratio, sintering atmosphere, sintering temperature, and the structural state of the resistivity and material constants with the material composition varies. Now also appears to the silicon carbide, selenium, tin, tantalum nitride, etc. as the representative of the non-oxide-based NTC thermistor material.

NTC thermistor semiconductive porcelain mostly spinel structure or other structure of the oxide ceramics, having a negative temperature coefficient, the resistance value can be approximated as:

Formula RT RT0 is the temperature T, T0 when the resistance value, Bn is a material constant. Ceramic grain changes due to temperature changes in the resistivity, which is determined by the semiconductor properties.

NTC negative temperature coefficient thermistor History

The NTC thermistor experienced long stage. 1834, the first time scientists have found that the characteristics of the negative temperature coefficient of silver sulfide. In 1930, scientists found that the cuprous oxide - copper oxide has a negative temperature coefficient of performance and the success of the use of in aviation instrument temperature compensation circuit. Subsequently, due to the continuous development of transistor technology, thermistor made significant progress. NTC thermistor developed in 1960.

NTC negative temperature coefficient thermistor temperature range

Its measurement range is generally -10 ~ +300 ℃, can also be done from -200 to +10 ° C, and even can be used for temperature measurement with +300 ~ +1200 ℃ environment.

The negative temperature coefficient thermistor thermometer accuracy can reach 0.1 ° C temperature sensing less time to 10s. It is not only applicable to the granary thermometer, also can be used in food storage, medicine and health, scientific farming, marine, deep wells, high-altitude, glacier temperature measurement.

Edit this paragraph NTC characteristic curve

  NTC characteristic graph

NTC characteristic graph(Metal Oxide Varistor)

[1]

Edit this paragraph jargon

NTC negative temperature coefficient thermistor jargon

Zero-power resistance value RT (Ω)

RT refers to the predetermined temperature T, caused by changes in the resistance value can be ignored without taking into account the measured power of the measured resistance values ​​with respect to the total measurement error.

The resistance value and the temperature changes in the relationship of the formula:

RT = RN expB (1 / T - 1/TN)

RT: NTC thermistor resistance when the temperature T (K).

RN: NTC thermistor resistance rated temperature TN (K).

T: predetermined temperature (K).

B: NTC thermistor material constant, known as thermal index.

exp: natural number e base index (e = 2.71828 ...).

This relationship is the empirical formula, only within the limited range of the nominal or rated temperature TN resistance RN having a reasonable degree of accuracy, because the material constant B itself is also a function of the temperature T.

Rated zero power resistance value of R25 (Ω)

Rated zero power resistance value of the NTC thermistor resistor R25 measured at the reference temperature of 25 ℃, the resistance value is NTC thermistor nominal resistance value according to the provisions of the GB. Commonly referred to as the NTC thermistor much resistance, and also refers to the value.

Material constants (thermal index) B value (K)

B value is defined as:

RT1: zero-power resistance value when the temperature T1 (K).

RT2: zero-power resistance value when the temperature T2 (K).

T1, T2: two specified temperature (K).

Common NTC thermistor B value range between 2000K ~ 6000K.

Zero power temperature coefficient of resistance (αT)

Zero Activity of relative change of the power resistance value of the NTC thermistor at a predetermined temperature, causing the ratio of the value of the temperature change of the change.

αT: zero power when the temperature T (K) resistance temperature coefficient.

RT: zero-power resistance value when the temperature T (K).

T: temperature (T).

B: material constants.

Dissipation factor (δ)

, NTC thermistor dissipation factor is the ratio of the corresponding temperature change of the power dissipated in the resistance change and the resistance body in a predetermined ambient temperature.

δ: NTC thermistor dissipation factor (mW / K).

The △ P: NTC thermistor consumption of power (mW).

△ T: the NTC thermistor consumption power △ P, the corresponding temperature change of the resistance body (K).

Thermal time constant (τ)

Zero-power conditions, When mutations temperature, the temperature of the thermistor changes the time required in the beginning not two temperature difference of 63.2%, the thermal time constant and the NTC thermistor is proportional to the thermal capacity, and its dissipation coefficient inversely proportional.

τ: thermal time constant (S).

C: NTC thermistor heat capacity.

δ: NTC thermistor dissipation coefficient.

Rated power Pn

Thermistor technical conditions prescribed long-term continuous work allowed power consumption. In this power, the resistor body temperature does not exceed its maximum operating temperature.

Maximum working temperature Tmax

Thermistor technical conditions prescribed long-term continuous work the maximum temperature allowed. Namely:

T0-ambient temperature.

Measuring power Pm

Thermistor at a predetermined ambient temperature of the resistive element by measuring current of the resistance change caused by heating with respect to the total measurement error is negligible power consumption.

General requirements for the resistance change is greater than 0.1%, then the measured power Pm is:

Resistance temperature characteristic

NTC thermistor temperature characteristics can be approximated by:

Formula:

RT: temperature T, the zero-power resistance value.

A: with the the thermistor material physical characteristics and geometry of the coefficient.

B: B values.

T: temperature (k).

The more accurate expression:

Formula:

RT: thermistor temperature T, the zero-power resistance value.

T: absolute temperature value, K;

A, B, C, D: for a specific constant.

R-T characteristics of the NTC negative temperature coefficient thermistor

B the same value, different resistance RT characteristic curve diagram

Same resistance and B value of the NTC thermistor RT characteristics curve diagram

Temperature measurement and control with NTC thermistor

Overall structure

Epoxy package series NTC thermistor

The glass encapsulation Series NTC thermistor

Application circuit schematics

Temperature measurement (Wheatstone bridge circuit)

Temperature control

Application Design

Electronic thermometer, electronic calendar, electronic clock temperature display, electronic gifts;

Heating and cooling equipment, heating thermostat electrical appliances;

Automotive electronic temperature measurement and control circuit;

Temperature sensor, temperature instrumentation;

Medical electronic equipment, electronic washing equipment;

Mobile phone batteries and charging appliances.(Metal Oxide Varistor)

What is the role of the thermal resistance?

Including a positive temperature coefficient (PTC) thermistor(Metal Oxide Varistor), and a negative temperature coefficient (NTC) thermistor.

The thermistor major characteristics: (1) high sensitivity, temperature coefficient of resistance than metal 10 to 100 times more; ② Operating temperature range is wide, the room temperature device is suitable for -55 ° C to 315 ° C, high-temperature devices applicable to a temperature higher than 315 ℃ (the highest can reach 2000 ℃) the cryogenic devices applicable to -273 ℃ to 55 ° C; prefectural - level small size, capable of measuring the gap can not be measured by other thermometer, the temperature of the cavity and in vivo vascular; ④ easy to use, the resistance value can be 0.1 ~ 100kΩ arbitrary choice; ⑤ easily processed into complex shapes, can be mass; ⑥ stability is good, strong overload.

Due to the unique properties of semiconductor thermistor, so in terms of application, it not only can be used as the measuring element (such as measuring temperature, flow, level, etc.), can also be used as a control element (such as thermal switches, current limiter) and circuit compensation components. The thermistor is widely used in household appliances, electric power industry, telecommunications, military science, aerospace and other fields, extremely broad prospects for development.

A PTC thermistor(Metal Oxide Varistor)

PTC (Positive Temperature Coeff1Cient) refers to a sharp increase in resistance at a certain temperature, the phenomenon or materials having a positive temperature coefficient thermistor can be specifically used as a constant temperature sensor. The material is based on BaTiO3 or SrTiO3 or PbTiO3 as the main component of the sintered body, wherein the incorporation of a trace amount of Nb, Ta, Bi, Sb, Y, La and other oxides the valence control leaving half of conductivity, normally this The semiconductor of BaTiO3 and other materials referred to as the semiconductive porcelain (body); also added to increase its positive temperature coefficient of resistance, Mn, Fe, Cu, Cr oxide of additives and from other effects, using the general ceramic process forming The high temperature sintering the such as leaving titanate platinum semiconducting its solid solution, to thereby obtain the positive characteristics thermistor material. Its temperature coefficient and Curie point temperature varies with the composition and sintering conditions (especially cooling temperature).

Barium titanate crystals belong to the perovskite-type structure, which is a ferroelectric material, pure barium titanate is an insulating material. Adding small amounts of rare earth elements, in the barium titanate material, after appropriate heat treatment, in the vicinity of the Curie temperature, the resistivity increased sharply by several orders of magnitude to produce the PTC effect, this effect and BaTiO3 crystal ferroelectric properties in the vicinity of the Curie temperature related to the phase change of the material. The barium titanate semiconductive ceramic is a polycrystalline material, the interface between the grains exist between the grains. The semiconductive porcelain when it reaches a certain temperature or voltage, the crystal grain boundary changes, so that the resistance sharply changes.

Barium titanate semiconductor ceramic PTC effect due to the grain boundary (grain boundaries). The interface is equivalent to a potential barrier for the conduction electron, intergranular. The temperature is low, due to the effect of electric field within the barium titanate, resulting in electrons very easily across the barrier, then the resistance value is small. When the temperature is raised to the Curie point temperature (i.e., the critical temperature) near the inner electric field is damaged, it does not help the conduction electrons across the barrier. This corresponds to the barrier rises, the resistance value increases suddenly, to generate the PTC effect. The physical model of the PTC effect of barium titanate semiconductor ceramic the sea looking surface barrier model, Daniels et al the barium absence of models and superimposed barrier model, they were from different aspects of the PTC effect made a reasonable explanation.

PTC thermistor appeared in 1950, and then 1954 to barium titanate as a main material of the PTC thermistor. PTC thermistor in the industry can be used as a measurement and control of temperature, temperature detection and regulation is also used in certain parts of the car, but also a large number for civilian equipment, such as water temperature control instant water boiler, air-conditioner and the temperature of the cold storage itself heating for gas analysis and wind machine.

PTC thermistor In addition to its use as a heating element, but also play the role of the "switch", both sensitive element, heater and switch three functions, called "thermal switch. Current caused by the components after the temperature rise, i.e. the increase in the temperature of the heating element, when the temperature exceeds the Curie point, the resistance is increased, thus limiting the current increases, then the current causes lower element temperature decreases, the resistance value decreases so that the circuit current increases, the element temperature rises again and again, so it has to keep the temperature in a specific range of function, but also play the switching action. Made of such a resistance temperature characteristic heating source applications as the heating element, air heater, electric iron, drying closet, air conditioning, etc., but also electrical played overheating protective effect.

NTC thermistor(Metal Oxide Varistor)

NTC (Negative Temperature Coeff1Cient) refers to the reduced resistivity exponential relationship, with a temperature rise phenomenon and material having a negative temperature coefficient thermistor. The material is sufficiently mixed with manganese, copper, silicon, cobalt, iron, nickel, zinc, and the like of two or more metal oxides, molding and sintering process is made of a semiconductor ceramic having a negative temperature coefficient, can be made (NTC) thermistor. Its resistivity and material constants with the material composition ratio, sintering atmosphere, sintering temperature, and the structural state varies. Now also appears to the silicon carbide, selenium, tin, tantalum nitride, etc. as the representative of the non-oxide-based NTC thermistor material.

The NTC thermistor experienced long stage. 1834, the first time scientists have found that the characteristics of the negative temperature coefficient of silver sulfide. In 1930, scientists found that the cuprous oxide - copper oxide has a negative temperature coefficient of performance and the success of the use of in aviation instrument temperature compensation circuit. Subsequently, due to the continuous development of transistor technology, thermistor made significant progress. Developed in 1960 the NTC thermistor, widely used for temperature measurement, temperature control, temperature compensation.

Measuring it is generally in the range of -10 to +300 ° C and -200 to +10 ° C, can also be done.

The thermistor thermometer accuracy can reach 0.1 ° C temperature sensing less time to 10s. It is not only applicable to the granary thermometer, also can be used in food storage, medicine and health, scientific farming, marine, deep wells, high-altitude, glacier temperature measurement.(Metal Oxide Varistor)