Power adapters ​Common troubleshooting

Power adapters:  It is a power supply conversion equipment for small portable electronic equipment and electronic appliances. It is generally composed of shell, power transformer and rectifier circuit. According to its output type, it can be divided into AC output type and DC output type. According to the connection mode, it can be divided into plug-in type and desktop type. It is widely used in telephone mothers, game consoles, language repeaters, walkman, notebook computers, cellular phones and other equipment.
Power adapters Common troubleshooting:
1, line fault
Line failure, including poor power line failure, poor contact oxidation contact, and so on. Check whether the input and output lines are energized.
If the line fails, 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:
A switching power supply load short-circuit fault (especially DC/DC converter short-circuit or poor performance), at this time, first disconnect all loads of the switching power supply circuit, check whether the switching power supply circuit fault or load circuit fault. If the load circuit is disconnected and the voltage output is normal, it means that the load is too heavy or that the switching power supply circuit is still abnormal.
B output voltage terminal filter capacitor or rectifier diode failure can be judged by replacement method.
The performance of c-switch is degraded, which leads to the failure of normal conduction of the switch, increases the internal resistance of the power supply and decreases the load capacity. The bad d-switching transformer not only causes the drop of output voltage, but also causes the insufficient excitation of switching tube, which damages the switching tube.
C 300V filter capacitance is poor, resulting in poor power load capacity, the output voltage of one load will drop.
3, the output voltage is too high.
The high output voltage generally comes from the voltage sampling and voltage stabilizing control circuit. In the closed control loop composed of DC output, sampling resistance, error sampling amplifier such as TL431, optocoupler, power control chip, etc., any problem of any part will cause the output voltage to rise.
4, the safety valve is normal, no output voltage.
The safety valve is normal, and no output voltage indicates that the switching power supply is not working or entering the protection state. The first step is to check the start-up voltage of the start-up foot of the power supply control chip. If there is no start-up voltage or the start-up voltage is too low, then check whether the external components of the start-up foot and the start-up resistance are leakage.
If the power control chip is normal, the fault can be found quickly through the above monitoring. If there is starting voltage, the output terminal of the control chip will be measured whether there is a jump of high and low levels at the moment of starting. If there is no jump, it will indicate that the control chip is damaged, the peripheral oscillating circuit components are damaged or the protection circuit is faulty. The control chip will be replaced and the peripheral components will be checked one by one. The number of cases is poor or damaged.
5, the insurance burns or explode.
Mainly check rectifier bridge, diode, switch tube and 300 volt on the large filter capacitor and other parts. Cause the insurance to burn, blacken, may also be the problem that the interference circuit causes. Particularly noteworthy is that due to the breakdown of the switch tube, it usually burns down the power control chip and the current detection resistance. Thermistors are also easily burned together with the insurance.