ZINC OXIDE VARISTOR
1) Are non-liner resistors utilize a semiconductor electronic ceramic element
Mainly composed of Zinc Oxide and its resistors change as a function of the
Applied voltage. It's called varistor or Transient surge absorbers.
2) Features
Widely voltage 18v-1.8kv;
Fast response to the rapidly increase voltage(≤ 25ns);
Excellent non-linearity votage;
Symmetric V-I characteristics;
Great withstanding surge current(2000A/cm2);
No follow-on current;
Long life;
3)How to select a varistor(only reference)
A: Varistor voltage
Varsto voltage should be more than the operating voltage in over protective
Circuit, the formula is shown as the follow.
V1mA=a. V/b. C
A-power Voltage ripple coefficient usually 1.2;
V-DC Voltage (significant value only AC power);
B-Tolerance usually take 0.85
C-Ageing coefficient usually take 0.9
B: Withstanding surge current
In general, withstanding surge current is max, Pulse current value which determined by test conditions such as wave-shape, amplitude and intermal time, when the amplitude decrease to 50% of the initial, it should be increased to 2 times of the initial in order to keep the life longer, the surge current which is absorbed by the varistor should be less than max.