1. If there is a load short circuit fault in the switching power supply (especially a short circuit or poor performance of the DC/DC converter), first disconnect all loads in 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; If it is still abnormal, it indicates that there is a malfunction in the switch power circuit.

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

3. The performance of the switch tube decreases, resulting in the inability of the switch tube to conduct normally, increasing the internal resistance of the power supply and reducing the load capacity.

4. Poor switching transformers not only cause a decrease in output voltage, but also result in insufficient excitation of the switch tube and damage to the switch tube.

5. Poor 300V filtering capacitor results in poor load carrying capacity of the power supply, and the output voltage will decrease once the load is connected.

Output voltage too high

The high output voltage generally comes from the voltage stabilization sampling and voltage stabilization control circuit. In a closed control loop composed of DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip, etc., any problem with any of the components will cause an increase in output voltage.

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 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 the external components and starting resistance of the starting pin for leakage.

If the power control chip is normal, the fault can be quickly detected through the above monitoring. If there is a startup voltage, measure whether there is a high or 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. Replace the control chip, check the peripheral components, and check them one by one; If there is a jump, most cases are due to poor or damaged switch tubes.

Mainly inspect the rectifier bridge, various diodes, switch tubes, and large filtering capacitors on 300V. Causing fuse burning and blackening may also be caused by issues with anti-interference circuits. It is particularly noteworthy that the fuse burns out due to the breakdown of the switch tube, which usually burns out the power control chip and current detection resistor. Thermistors are also easily burned out along with the fuse.