Ding Lixun organizes the following as the main reason for the low output voltage caused by the power adapter, we can be used as a reference:

1. Switching power supply load short-circuit fault (especially short-circuit or poor performance of DC/DC converter, etc.) At this time, first turn off all loads of the switching power supply circuit and check whether the switching power supply circuit is faulty or the load circuit is faulty. If the load circuit is disconnected and the voltage output is normal, it indicates that the load is too heavy; or it still does not indicate that the switching power supply circuit is faulty.

2, the output voltage filter capacitor or rectifier diode failure, etc., can be judged by the replacement method.

3, the performance of the switch tube is reduced, resulting in the switch tube can not be normally turned on, so that the internal resistance of the power supply increases, the load capacity decreases.

4. The bad transformer of the switch not only causes the output voltage to drop, but also causes the insufficient activation of the switch tube and damages the switch tube.

5, 300V filter capacitor is bad, causing the power to carry the load capacity is poor, a load output voltage will drop.

The output voltage is too high

The output voltage is too high generally from the regulator sampling and regulator control circuit. In the closed control loop formed by the circuits such as the DC output, sampling resistors, and error sampling amplifiers such as the TL431, optocoupler, and power supply control chip, any problem with any part will cause the output voltage to rise.

The fuse is normal and there is no output voltage

The fuse is normal and no output voltage indicates that the switching power supply is not working or has entered the protection state. The first step is to check the value of the start voltage of the power control chip's start pin. If there is no start voltage or the start voltage is too low, check the external components of the start pin and the start resistor for leakage.

If the power supply control chip is normal, the fault can be quickly found through the above-mentioned monitoring. If there is a starting voltage, then whether there is a high or low level jump at the output end of the measurement control chip is detected. If there is no jump, it indicates that the control chip is damaged, the peripheral oscillation circuit element is damaged, or the protection circuit is faulty, and the control is replaced. The chip, check the external components, check one by one; if the jump, most of the cases are bad or damaged switch.

Insurance burned or blown

Mainly check rectifier bridges, diodes, switch tubes, and large filter capacitors on 300 volts. Causes the insurance to burn, black, it may also be caused by problems with the anti-interference circuit. In particular, it is worth noting that due to the breakdown of the switch tube, the power supply control chip and the current detection resistor are usually burned. The thermistor is also easily burned together with the fuse.