Power adapter caused by the main reason for low output voltage
2022-09-20 Views：31
1, the power adapter load short-circuit fault (especially DC/DC converter short-circuit or poor performance, etc.), at this time, first disconnect all the loads of the switching power supply circuit, check whether the switching power supply circuit failure or load circuit has a fault. If the load circuit is disconnected and the voltage output is normal, it means that the load is too heavy; or still not normal means that the switching power supply circuit is faulty.
2, the output voltage terminal filter capacitor or rectifier diode failure, etc., can be judged by the replacement method.
3, the performance of the switching tube decline, 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 to drop, while causing insufficient excitation of the switching tube thus damaging the switching tube.
5, 300V filter capacitor is bad, resulting in poor power supply with load capacity, a load will be connected to the output voltage will drop.
Output voltage is generally too high from the regulated sampling and voltage control circuit. In the DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits together constitute a closed control loop, any one of the parts of the problem will cause the output voltage to rise.
Fuse 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 start voltage value of the start pin of the power control chip, if there is no start voltage or start voltage is too low, then check the start pin external components and start resistor for leakage.
If the power supply control chip is normal, the above monitoring can quickly find out where the fault lies. If there is a start voltage, then measure the output of the control chip in the moment of power on whether there is a high, low level jump, if no jump, indicating that the control chip is damaged, peripheral oscillation circuit components damage or protection circuit failure, by replacing the control chip, check the peripheral components, check one by one; if in the jump, most cases for the switch tube is bad or damaged.
Insurance burned or blown, mainly check the rectifier bridge, each diode, switching tubes and 300 volts on the large filter capacitors and other parts. Resulting in insurance burn, black, may also be caused by anti-interference circuit problems. Particularly noteworthy: insurance burn due to switch tube breakdown, usually burn the power control chip and current detection resistor. The thermistor is also easy to be burned together with the insurance.
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