Common problems and solutions of power adapter

1、 Line problems

Circuit problems, including power line damage and power failure, poor DC head contact, etc. Check whether the input line and output line can be powered on normally.

In case of line fault, it can be solved by replacing DC line or AC line.

2、 Output voltage too low

The following are the main causes of low output voltage:

1. In case of power load short-circuit fault (especially dc/dc converter short-circuit or poor performance, etc.), first disconnect all loads of the power circuit and check whether the switching power circuit is faulty or the load circuit is faulty. If the load circuit is disconnected and the voltage output is normal, the load is too heavy; Or it is still abnormal, indicating that there is a fault in the switching power supply circuit.

2. Failure of filter capacitor or rectifier diode at output voltage terminal can be judged by replacement method.

3. The performance of the switch tube is degraded, resulting in the switch tube can not be connected normally, which increases the internal resistance of the power supply and reduces the load capacity.

4. The poor switch transformer not only causes the output voltage to drop, but also causes insufficient excitation of the switch tube, thus damaging the switch tube

5. The 300V filter capacitor is poor, resulting in poor load capacity of the power supply, and the output voltage will drop once the load is connected.

3、 Output voltage too high

High output voltage usually comes from stabilized voltage sampling and stabilized voltage control circuit. In the closed control loop composed of DC output, sampling resistance, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, the output voltage will rise if any part fails.

4、 Fuse tube is normal without output voltage

The fuse tube 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 starting voltage value of the starting pin of the power control chip. If there is no starting voltage or the starting voltage is too low, check whether the external components of the starting pin and the starting resistance have leakage.

If the power control chip is normal, the fault can be quickly found through the above monitoring. If there is starting voltage, measure whether there is high-level and low-level jump at the output end of the control chip at the moment of startup. If there is no jump, it indicates that the control chip is damaged, the peripheral oscillation circuit components are damaged or the protection circuit is faulty. Check one by one by replacing the control chip and checking the peripheral components; In case of jump, the switch tube is poor or damaged in most cases.

5、 The fuse burns or blows up

Mainly check the rectifier bridge, diodes, switches and large filter capacitors on 300V. The fuse may be burnt or blackened, or it may be caused by problems in the anti-interference circuit. In particular, it is worth noting that the fuse burns due to the breakdown of the switch tube, which usually burns out the power control chip and the current detection resistance. Thermistor is easy to burn out together with fuse.