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)
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