Surge protector design principles, characteristics, use areas

 Design Principles
In the most common in the surge protection device, there is one known as the element of the metal oxide varistor (Metal Oxide Varistor, MOV), and used to transfer the excess voltage. As shown in the following figure, MOV FireWire and ground connections.
MOV is composed of three parts: the middle is a metal oxide material, and connected to power supply and ground lines by two semiconductor.
These semiconductor having a variable resistor with the voltage change. Will generate a very high resistance when the voltage is below a certain value, the motion of electrons in the semiconductor. Conversely, when the voltage exceeds the specified value, the electronic games change, the semiconductor resistor will be substantially reduced. If the voltage is normal, MOV busy at the side. When the voltage is too high, MOV can conduct a lot of current to eliminate the excess voltage. Live voltage will return to normal as the excess current MOV transferred to the ground, causing MOV resistance increases rapidly again. In this manner, MOV only transfer the surge current, while allowing standard current to continue to supply power for the connected device and the surge protection device. So to speak, the MOV role like a pressure-sensitive valve will open only when the pressure is too high.
Another common surge protection device is a gas discharge tube. The role of these gas discharge tubes and MOV same - they will be the excess current from FireWire to ground, to achieve this function by using an inert gas between the two wires as the conductor. When the voltage is in a specific range, the composition of the gas determines that it is a poor conductor. If voltage surges and more than this range, the intensity of the current will be sufficient so that the gas ionization, so that the gas discharge tube to be very good conductor. It will be current conduction to the ground until the voltage is restored to normal levels, then it will become a poor conductor.
Both methods are based on the parallel circuit design - excess voltage from standard circuit into another circuit. Several surge protection products using a series circuit designed suppressing surge - they are not the excess current is diverted to another line, but by reducing the flow through the line of fire power. Basically, these suppressor stored electrical energy to the high voltage is detected, followed by gradually releasing them. The manufacture of such protection company explained that the method can provide better protection, because it reacts faster, and will not be diverted to the ground, but on the other hand, this shunt may interfere with the building's electricity system.
Suppression diodes: suppression diode clamp pressure limiting function, it is working in reverse breakdown region, because it has a low clamping voltage and actions in response to the advantage of faster, especially suitable for use as a multi-level protection circuit in the last few levels protection components. Suppression diode in the region of breakdown voltage characteristics can be represented by the formula: I = CUα above formula in which α is the nonlinear coefficient, for homogeneous zener diode α = 7 to 9, in the the avalanche diode α = 5.
 suppression diode technology parameters:
(1) of the rated breakdown voltage, it is in the specified reverse breakdown current (often LMA) under the breakdown voltage of the Zener diode breakdown voltage rating generally in the range of 2.9V ~ 4.7V, and avalanche diode rated breakdown voltage is often in the range of 5.6V ~ 200V.
    (2) The maximum clamping voltage: It refers to the tube in a large current through a predetermined waveform, the maximum voltage appearing across.
    (3) pulse power: it is the plot of the current equivalent of the tube ends maximum clamping voltage of the tube under the provisions of the current waveform (10/1000μs).
    (4) Reverse Variable bit voltage: it refers to the maximum voltage of the tube in the reverse leakage area, the ends can be applied in the tube should not be at this voltage breakdown. The reverse displacement voltage should be significantly higher than the maximum operating voltage spikes protect electronic systems, that is not the normal operation of the system is weak conduction state.
    (5) Maximum leakage current: it refers to the maximum reverse current reverse displacement voltage is applied, the tube flowing.
    (6) Response time :10-11us
As auxiliary components, some surge protector comes with built-in fuse. Fuse is a resistor, when the current is less than a standard, it's a very good conductive properties. Conversely, when the current exceeds the acceptable standard, the resistance of the heat generated will blow the fuse, thereby cutting off the circuit. MOV(metal oxide varistor) can not suppress surges, excessive current will blow the fuse to protect the connected equipment. The fuse only be used once, once blown, it needs to be replaced.
 SPD front-end fuse should be installed in accordance with the parameters of the arrester manufacturers.
If manufacturers do not provide general selection principles:
(Maximum surge protector fuse strength A) and (to access maximum supply current distribution lines B) to determine the (switch or fuse breaking current C).
Determination:
When: B> A C less than or equal to A
When: B = A, C is less than A or not to install C
When: B <A, C is less than B or not to install C
Some surge protector with line conditioning system, used to filter out line noise, reducing current fluctuations. This basic system structure of the surge protection device is very simple. FireWire ring choke coil connected to the outlet of the power supply board. Choke coil is just a ring made of magnetic material, wrapped around the outside wire - basic electromagnet. The fluctuations give electromagnet current flows through the line of fire in charge, so that the issue of electromagnetic energy, thus eliminating the tiny fluctuations in the current. This "after adjustment" current is more stable, allows the supply current of the computer (or other electronic device) is more gentle.
In electronic design, the surge mainly refers to the power source (just mainly refers to the power supply) that has just opened momentary strong pulse, due to the nonlinearity of the circuit itself may be higher than the pulse of the power supply itself; or due to power supply or other parts of the circuit by itself or outside spikes interference called surge. It is likely that the circuit is burned in the surge of the moment, such as a PN junction capacitor breakdown resistance blown. Surge protection is nonlinear components sensitive design of the high-frequency (surge) protection circuit, simple, common size capacitor in parallel and series inductance.
 Classification of Surge Protection Device (SPD)
According to the principle:
(1) switch type: Its working principle is presented when there is no transient overvoltage is high impedance, but once the lightning transient overvoltage response, its impedance mutation to a low value, allow the lightning current through. The devices are used as such devices: a discharge gap, gas discharge tubes, thyristors, transistors, etc..
(2) the pressure limiting type: Its working principle is as high obstruction when no transient overvoltage, but with the increase of the surge current and voltage the impedance will continue to reduce its current-voltage characteristics of a strongly nonlinear. The devices used for such devices are: zinc oxide, varistor(metal oxide varistor), suppression diodes, avalanche diodes.
(3) shunt or choke-type
    Shunt: protected devices in parallel, the lightning pulse rendered as low impedance, and rendered the normal operating frequency is high impedance.
    The choke type: in series with the equipment to be protected, the lightning pulse is rendered as a high impedance, and the normal operating frequency is rendered as low impedance. The devices used for such devices: a choke coil, a high-pass filter, low pass filter, a wavelength of 1/4 short-circuit, etc..
    By Use:
(1) Power Protection: AC power protection, DC power protection, switch power protection.
 (2) signal protection: low-frequency signal protection, high-frequency signal protection, antenna protector.
To  surge protector and its application
1, the surge voltage
   Overvoltage circuit struck by lightning and often produce high when turned on, disconnect the inductive load or large load operation, this transient overvoltage (or overcurrent) called the surge voltage (or current surges), a transient disturbance: e.g. disconnected from the relay coil of DC 6V when there will be a surge voltage of 300V ~ 600V; turned incandescent occur when a surge current of 8 to 10 times the rated current; When connected large capacitive load, such as compensation capacitor bank, and often there will be a large inrush current impact sudden lowering of the supply voltage; When you disconnect the load transformer also occur up to 8 to 10 times the rated voltage operation voltage. Worsening phenomenon of surge voltage endanger the safety work of automation equipment, eliminating the surge noise interference to prevent surge damage has been running the core issues related to the safe and reliable automation equipment. The degree of integration of modern electronic equipment has been improving, but their ability to resist the surge voltage is on the decline. In most cases, the surge voltages may damage to the circuit and its components, the extent of damage and is closely related to the compressive strength of the components, and can convert the energy of the circuit.
   This surge voltage conductor in order to avoid the the surge voltage wreck sensitive automation equipment, must occur within a very short time with the potential equalization system short-circuited (the introduction of earth). In the discharge process, the discharge current can be up to several thousand amps, to At the same time, people tend to expect the protection unit in the discharge current is large, the output voltage can be limited to the lowest possible value. Accordingly, the air spark gap, inflatable overvoltage discharge appliances, varistors, avalanche diodes, the TVS (Transientvoltagesuppressor), FLASHTRAB VALETRAB, SOCKETTRAB, MAINTRAB other components, is used alone or in the form of a combining circuit is applied to the circuit to be protected , because of their respective different characteristics of each component, and having different properties: the discharge capacity; response characteristics; arc performance; pressure limiting accuracy. Combined in accordance with the characteristics of the various types of products according to the requirements of different applications as well as equipment for surge voltage protection, over-voltage protection systems meet the application requirements.(metal oxide varistor)