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# Understanding the nominal characteristic parameters of varistor

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Nominal parameters of varistor:

Varistors are represented by the letter "my", if J is added to the household, The letters W, G, P, L, H, Z, B, C, N, K are used for voltage stabilization, overvoltage protection, high frequency circuit, lightning protection, arc extinguishing, noise elimination, compensation, demagnetization, high energy or high reliability respectively. Although varistors can absorb large surge energy, they cannot withstand sustained currents above milliamperes, which must be taken into account when being used as overvoltage protection.

The varistor characteristic parameters are as follows:

1) Voltage-sensitive voltage UNGU1mAN: a voltage commonly used to indicate whether a varistor is on or off when it passes through the 1mA DC current on a varistor, and this voltage is known as a varistor voltage UN. The voltage-sensitive voltage is also represented by the symbol U1mA. The error range of voltage-sensitive voltage is generally ±10%. In the test and practical application, the 10% reduction of the voltage sensitivity from the normal value is usually taken as the criterion for the failure of the varistor.

2) Continuous operating voltage UC: refers to the AC voltage (effective value) Uac or DC voltage Udc that the varistor can withstand for a long time. Generally Uac≈ 0.64U1mA, Udc≈ 0.83U1mA.

3)Flow rate (Impulse current IP: refers to the peak impulse current of 8 / 20 μ s wave that the varistor can withstand. "can withstand" means that the variable-rate of the voltage-sensitive voltage after shock is not more than 10%. The current technical specifications usually give an IP value that impacts once.

.4) Clamping voltage (limited voltage VC: the clamping voltage given in the technical specification refers to the voltage presented on the varistor when a specified 8 / 20 μ s wave impulse current IXA is applied to the varistor). In practical use, the higher the voltage-sensitive voltage, the greater the impulse current applied, and the higher the limiting voltage (or residual voltage), which can be found from the V-I curve given by the product.

5) Rated energy E: rated energy refers to the energy of a varistor capable of withstanding the impulse current of a specified waveform at a time (the variable-rate of the variable-voltage after shock is not greater than 10).

6) Rated power (mean power Pm: the average power that a varistor can withstand if it is subjected to multiple shocks at room temperature and has a short interval between shocks, thus having a heat accumulation effect. Although varistors can withstand large pulse powers, the average power they can withstand is small.

7) Capacitance C0: refers to the capacitance exhibited between the two electrodes of the varistor, in the range of several pF to several hundred nF. The smaller the volume is and the higher the varistor voltage is,the smaller the capacitance will be.