USB charger Overvoltage protection
A varistor in a charger circuit
Varistor is a voltage-sensitive resistor abbreviation, the English abbreviation for the VSR (Voltage-sensitive Resistor), also known as metal oxide varistor (Metal-oxide Varistor, MOV). It belongs to an over-voltage protection components, the resistance The value varies with the terminal voltage. The main features of the varistor is a wide range of operating voltage (6V ~ 3000V, divided into several files), the corresponding over-voltage pulse fast (a few nanoseconds to tens of nanoseconds), the ability to withstand the impact of a strong current (up to 100A (Less than 0.05% / ℃), and low price, small size, mainly used in the charger to absorb the surge voltage (less than 0.05% / ℃), low leakage current (less than a few microamps to several tens of microamps) The Voltage protection, lightning protection, suppression of inrush current, absorption of spikes, limiting, high voltage arc suppression, noise reduction, protection of semiconductor components and so on.
A varistor is an element with a transient voltage suppression function that can be used in place of a combination of transient suppression diodes, zener diodes, and capacitors. The varistor protects the integrated circuit IC and other semiconductor components in the charger circuit from damage caused by electrostatic discharge, surge and other transient currents such as lightning strikes. Use only the varistor and then connected to the protected IC or charger AC input circuit, when the voltage instantly higher than a certain value, the varistor resistance drops rapidly, conduction of high current, thus Protection IC or electrical equipment; when the voltage is lower than the varistor operating voltage, the varistor resistance is extremely high, almost open, and thus will not affect the normal operation of the device or charger.
There are three main parameters of the varistor: ① nominal voltage U1mA, when through the 1mA DC current, the voltage across the component; ② leakage current, it means that when the voltage across the device is equal to 75% U1mA, the components passed Of the DC current; ③ the flow rate, which indicates the maximum time within the specified time (8/20 micro), allowing the current through the pulse, where the pulse current from 90%. Up to Up time is 8 microseconds and peak duration is 20 microseconds.
Charger input protection circuit Commonly used varistor nominal voltage of 275VAC or 320VAC.
With the continuous progress of electronic technology, smart phones, tablet PCs, digital cameras, MP3 players and personal digital assistants (PDA) and other portable devices market continued rapid development, the use of more and more, so in the drive of these technology products Led the development of its peripheral products. One of the most rapid development of USB charger, because the USB charger, power adapter is the main power of these high-tech products.
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