What are the common reasons for power adapter failure?

　　I believe everyone is familiar with power adapters. I don’t know how much you know about the common causes and troubleshooting methods of power adapter failures. Now Wentong Electronics editor will let you know about it.

　　Common faults and troubleshooting methods of power adapters

　　1. Line failure

　　Line faults, including damage to the power cord, no power supply, poor contact port oxidation, etc. Focus on checking whether the input line and output line are powered on.

　　If the line is faulty, it can be solved by replacing the power cord.

　　2. The output voltage is too low

　　The following are the main reasons for low output voltage:

　　2.1 Switching power supply load short circuit fault (especially DC/DC converter short circuit or poor performance, etc.), at this time, 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, it means that the load is too heavy; or if it is still abnormal, the switching power supply circuit is faulty.

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

　　2.3 The performance of the switch tube is degraded, which causes the switch tube to fail to conduct normally, which increases the internal resistance of the power supply and reduces the load capacity. 2.4 The poor switching transformer will not only cause the output voltage to drop, but also cause insufficient excitation of the switching tube, which will damage the switching tube. 2.5 The poor 300V filter capacitor will cause the power supply to have poor load capacity, and the output voltage will drop as soon as the load is connected.

　　3. The output voltage is too high

　　The high output voltage generally comes from the voltage-stabilizing sampling and voltage-stabilizing control circuits. In the closed control loop formed by the DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, any problem in any of these parts will cause the output voltage to rise.

　　Fourth, the fuse is normal, no output voltage

　　The fuse is normal and no output voltage indicates that the switching power supply is not working or has entered a protection state. The first step is to check the value of the start-up voltage of the start-up pin of the power control chip. If there is no start-up voltage or the start-up voltage is too low, check whether the external components of the start-up pin and the start-up resistor are leaking.

　　If the power control chip is normal, the fault can be quickly found through the above monitoring. If there is a start-up voltage, measure whether there is a jump between high and low levels at the output end of the control chip at the moment of booting. If there is no jump, it means that the control chip is damaged, the peripheral oscillation circuit components are damaged or the protection circuit is faulty. Chip, check peripheral components, check one by one; if it is jumping, in most cases, the switch tube is bad or damaged.

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