What are the main causes of low output voltage caused by power adapters?

The following are the main reasons for low output voltage caused by power adapters:

1. Switching Power Supply load short circuit fault (especially DC/DC converter short circuit or poor performance, etc.), at this point, first disconnect all the load of the switching Power Supply circuit, check whether the switching power circuit fault or the load circuit fault. If the load circuit is disconnected and the voltage output is normal, it indicates that the load is too heavy. Or it is still abnormal, indicating that there is a fault in the switching power circuit.

2. Output voltage terminal filter capacitance or rectifier diode failure can be judged by substitution method.

3. The performance degradation of the switch tube leads to the failure of the normal conduction of the switch tube, which increases the internal resistance of the power supply and reduces the load capacity.

4. the switch transformer is not good, not only causes the output voltage to drop, but also causes the switch tube excitation is insufficient to damage the switch tube.

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

Too high output voltage
High output voltage usually comes from stabilized sampling and control circuit. In the dc output, sampling resistance, error sampling amplifier such as TL431, optocoupler, power supply control chip and other circuits together to constitute a closed control loop, any of the parts of the problem will cause the output voltage rise.

Fuse is normal, no output voltage
The fuse is normal and no output voltage indicates that the switching power supply is not working or in a protected 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, then check whether the components connected to the starting pin and the starting resistance leak electricity.

If the power control chip is normal, the fault can be detected quickly by the above monitoring. If there is starting voltage, measure whether the output end of the control chip has a high or low level jump at the moment of starting. If there is no jump, it indicates that the control chip is damaged, the peripheral oscillating circuit components are damaged or the protection circuit is in fault. Replace the control chip, check the peripheral components and check them one by one. If in the jump, most of the situation for the switch tube is bad or damaged.

Be sure to burn out or blow up
Mainly check the rectifier bridge, each diode, switch tube and the large filter capacitor on 300 volts. Lead to safety burn, blackening, may also be a problem with the anti-interference circuit. It is of particular interest that a safety fire due to a breakdown of the switch tube will usually burn out the power control chip and the current detection resistance. Thermistors also burn out easily with insurance.

Best Regards,

Ada Zheng