What are the factors that affect the power adapter voltage?

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

2. The failure of the filter capacitor or rectifier diode at the output voltage end can be judged by the replacement method.

3. The performance of the switch tube is degraded, resulting in the switch tube can not be turned on 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, thereby 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.

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.

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.

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.