Varistor in charger circuit
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Varistor in charger circuit
The varistor is the abbreviation of voltage-sensitive resistor. Its English abbreviation is VSR (Voltage-sensitive Resistor), also known as Metal-oxide Varistor (MOV). It belongs to an over-voltage protection component and its resistance. The value varies with the voltage of the terminal. The main characteristic of the varistor is that the working voltage range is wide (6V~3000V, divided into several gears), and the overvoltage pulse is correspondingly fast (a few nanoseconds to tens of nanoseconds), and the ability to withstand current is very strong (up to 100A). ~20kA), low leakage current (less than a few microamps to tens of microamps), low temperature coefficient of resistance (less than 0.05% / °C), and low price, small size, mainly used to absorb surge voltage in the charger . Over voltage protection, lightning protection, suppression of inrush current, absorption of spikes, limiting, high voltage arc extinguishing, noise cancellation, protection of semiconductor components and so on.
A varistor is a component with transient voltage suppression that can be used in place of a combination of a transient suppression diode, a Zener diode, and a capacitor. The varistor protects the integrated circuit IC and other semiconductor components in the charger circuit from damage caused by electrostatic discharges, surges, and other transient currents such as lightning strikes. When using, it is only necessary to connect the varistor to the AC input circuit of the protected IC or charger. When the voltage is higher than a certain value, the resistance of the varistor drops rapidly and turns on a large current. Protect the IC or electrical equipment; when the voltage is lower than the working voltage of the varistor, the varistor has a very high resistance value and is almost open, so it does not affect the normal operation of the device or the charger.
The main parameters of the varistor are three: 1 nominal voltage U1mA, the voltage value across the component when passing 1mA DC current; 2 leakage current, which means that when the voltage across the component is equal to 75% U1mA, the component passes DC current; 3-way flow, which indicates the maximum value of the pulse current allowed during the specified time (8/20 microseconds), where the pulse current is from 90%. The time from Up to Up is 8 microseconds and the peak duration is 20 microseconds.
The varistor commonly used in charger input protection circuits has a nominal voltage of 275VAC or 320VAC.