Switching power supply is the abbreviation of switching stabilized linear power supply. The previous power products used linear power supply, which is a transistor linear stabilized power supply, which has been gradually replaced by switching power supply due to low efficiency and other reasons. Switching power supply, as the name implies, is a power supply that maintains a stable output voltage by controlling the on time and off time of the switch tube. It has gradually developed in the direction of miniaturization, efficiency, modularity, and high reliability.
For switching power supplies, the input protection circuit is very important. The switching input protection circuit has functions such as overcurrent protection, overvoltage protection, and surge suppression. It plays a vital role in the voltage shock of the power grid and EMC. Here are six types of switching power supply input protection circuits:
1. Fuse form
There are ordinary and fast fuses, which have the characteristics of low melting point and fast fusing speed, but sparks and smoke will be generated when fusing, and even glass tubes will burst, so the safety is poor. The input protection circuit with only the fuse has only overcurrent protection. Generally, the actual fusing current when selecting the fuse is about 1.5 times the rated current.
2. Forms of fuse and varistor
This circuit has more varistors. The varistor specifications are 07471, 10471, 14471, etc., with surge suppression functions. Therefore, this circuit has overvoltage and overcurrent protection functions, and some also have lightning protection.
Three, fuse resistor, varistor form
Fuse resistors have the same function as fuses. They both provide over-current protection. But unlike fuses, they will not produce sparks and smoke when they are blown, which is safer in terms of safety. Varistors have surges. Voltage absorption, so this circuit form has overvoltage and overcurrent protection functions.
Four, fuse, NTC thermistor form
The thermistor uses a negative temperature coefficient, its resistance decreases with the increase of temperature, and it has the ability to suppress the inrush current of the circuit.
Five, varistor, NTC thermistor form
Six, fuse, varistor, NTC thermistor form
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