The main reasons for low output voltage caused by power adapter.

1, power adapter load short-circuit failure (especially DC/DC converter short circuit or poor performance, etc.), at this time, first disconnect all the load of the switching power supply circuit, check whether the switching power supply circuit failure or load circuit failure. If you disconnect the load circuit and the voltage output is normal, indicating that the load is too heavy; or still not normal switching power supply circuit failure.

2, the output voltage filter capacitor or rectifier diode failure, etc., can be replaced by the method of judgment.

3, the performance of the switching tube degradation, resulting in the switching tube can not be normal conduction, so that the internal resistance of the power supply increases, the load capacity decreases.

4, bad switching transformer, not only cause the output voltage drop, at the same time cause the switching tube excitation is not enough to damage the switching tube.

5, 300V filter capacitor is bad, resulting in poor power supply with load capacity, a connected load output voltage will drop.

Output voltage is generally too high from the regulator sampling and regulator control circuit. In the DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power supply control chip and other circuits constitute a closed control loop, any one of these parts have problems will cause the output voltage increases.

Fuse is normal, 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 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, then check whether the components connected to the start-up pin and the start-up resistor are leakage.

If the power control chip is normal, the above monitoring can quickly find the fault. If there is a start-up voltage, then measure the output of the control chip at the moment of power-on whether there is a high or low level jump, such as if no jump, indicating that the control chip is damaged, peripheral oscillator circuit components are damaged or the protection circuit is faulty, through the replacement of the control chip, check the peripheral components, one by one to check; if in the jump, most of the cases for the switching tube is bad or damaged.

Insurance burned or blown, mainly check the rectifier bridge, each diode, switching tube and 300 volts on the large filter capacitor and other parts. Caused by the insurance burn, black, may also be caused by problems with the anti-interference circuit. Particularly noteworthy is: due to the switching tube breakdown caused by the insurance burn, usually burn the power control chip and current detection resistor. Thermistor is also easy to be burned together with the insurance.

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