Common faults and maintenance methods of power adapters

1、 Circuit failure: Circuit failure, including power cord damage, no power supply, poor contact oxidation, etc. Focus on checking whether the input and output lines are powered on. If there is a circuit malfunction, it can be resolved by replacing the power cord or other means.

2、 The main cause of low output voltage is the following: 1. Short circuit fault of the switch power supply load (especially short circuit or poor performance of the DC/DC converter). At this time, first disconnect all loads in the switch power supply circuit and check whether the switch 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. If the filter capacitor or rectifier diode at the output voltage end fails, it can be judged through the replacement method. The performance of the 3 switch transistor decreases, resulting in the switch transistor not being able to conduct normally, increasing the internal resistance of the power supply and reducing the load capacity. Poor 4 switch transformer not only causes a decrease in output voltage, but also causes insufficient excitation of the switch tube, resulting in damage to the switch tube. The 5300V filter capacitor is poor, resulting in poor load carrying capacity of the power supply, and the output voltage will decrease once connected to the load.

3、 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.

4、 The fuse is normal and there is no output voltage. The fuse is normal and there is no output voltage, indicating that the switching power supply is not working or has entered a protective 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.

5、 The main inspection for burnt or blown out fuses is to inspect the rectifier bridge, diodes, switch tubes, and large filter capacitors on 300V. Causing fuse burning and blackening may also be caused by issues with anti-interference circuits. It is particularly important to note 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. That's all for the common faults and repairs of power adapters. In addition, we should pay attention to the daily maintenance and upkeep of power adapters, which can reduce the occurrence of faults and effectively extend their service life.