A varistor is a voltage-limiting protection device. Using the non-linear characteristics of the varistor, when the overvoltage appears between the poles of the varistor, the varistor can clamp the voltage to a relatively fixed voltage value, so as to achieve the protection of the back stage circuit. Main functions: overvoltage protection, lightning protection, inhibit surge current, absorb spike pulse, limiting, high-voltage arc extinguishing, noise suppression, protection of semiconductor components and so on. The main parameters are: varistor voltage, current capacity, junction capacitance, response time and so on.
The response time of the varistor is ns level, faster than the air discharge tube, slightly slower than the TVS tube (instantaneous suppression diode), generally used in electronic circuits for over-voltage protection and its response speed can meet the requirements.
Although the varistor can absorb a lot of surge energy, but can not withstand milliamperes above the continuous current, when used as overvoltage protection must take this into account. Selection of varistors, generally select the nominal voltage sensitivity V1mA and through-current capacity of two parameters.
1, a for the circuit voltage fluctuation factor, generally take the value of 1.2.
2, Vrms for the AC input voltage RMS.
3, b for the varistor error, generally take the value of 0.85.
4,C is the aging coefficient of the components, generally take the value of 0.9.
5. √2 is the peak-to-peak value to be considered in AC condition.
6,V1mA is the approximate value of the actual value of the varistor voltage.
7, throughput capacity, that is, the peak value of the pulse current is the ambient temperature of 25 degree , for the specified inrush current waveform and the number of specified inrush current, the variations in the varistor voltage does not exceed ± 10% of the pulse current value.
07D471K AC300V DC385 Voltage-sensitive power supply 470 (423-517) Limit power supply 775Vp (v) 10lp (A) Flow-through capacity 1200 1 time (A) 600 2 times (A) energy 30 0.25 power (W) 150 electric capacity 1KN Z (pF).
