Common issues with power adapters

Power adapters are electrical appliances that we use in our daily lives, but they may also encounter some minor malfunctions. Today, the editor has summarized some common malfunctions and repair methods. Let's take a look together!

1、 Line faults include damage to the power cord, lack of power supply, oxidation of the contact interface, and poor contact. 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 reason for low output voltage is due to a short circuit fault in the load of the switching power supply (especially a short circuit or poor performance of the DC/DC converter). At this time, first disconnect all loads in the switching power supply circuit and check whether it is a fault in the switching power supply circuit or the load circuit. 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 supply circuit. The failure of the filtering capacitor or rectifier diode at the output voltage terminal can be determined by the replacement method. The performance of the 3 switching tubes decreases, resulting in the inability of the switching tubes to conduct normally, increasing the internal resistance of the power supply and reducing the load capacity. The poor performance of the 4-switch transformer not only causes a decrease in output voltage, but also results in insufficient excitation of the switch tube, leading to damage to the switch tube. The 5300V filtering capacitor is poor, resulting in poor load carrying capacity of the power supply, and the output voltage will decrease once the load is connected.

3、 High output voltage generally comes from voltage stabilization sampling and voltage stabilization control circuits. 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 no output voltage indicates that the switch power supply is not working or has entered a protective state. The first step is to check the starting voltage value of the power control chip's starting pin. If there is no starting voltage or the starting voltage is too low, check whether the external components and starting resistance of the starting pin are leaking electricity. 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 there is a fault in the protection circuit. Replace the control chip, check the peripheral components, and check them one by one; If there is a jump, it is mostly due to poor or damaged switch tubes.

5、 The main inspection for burnt out or blown out insurance is to check the rectifier bridge, various diodes, switching tubes, and large filtering capacitors above 300 volts. Causing fuse burning and blackening may also be caused by problems with the anti-interference circuit. It is particularly important to note that the fuse burns out due to the breakdown of the switching tube, which usually burns out the power control chip and current detection resistor. Thermistors can also easily be 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.