The following are the main reasons for the low output voltage caused by the power adapter:

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 the switching power supply circuit, 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 it is still abnormal, indicating that the switching power supply circuit is faulty.

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

3. The performance of the switch tube decreases, resulting in the failure of the switch tube to be turned on normally, which increases the internal resistance of the power supply and decreases the load capacity.

4. The poor switching transformer not only causes the output voltage to drop, but also causes the switch tube to be excited insufficiently and damages the switch tube.

5. The 300V filter capacitor is poor, resulting in poor load capacity of the power supply, and the output voltage will drop as soon as the load is connected.

The output voltage is too high

Excessive output voltages typically come from regulated sampling and regulated control circuits. In a closed control loop composed of DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip, etc., a problem with any one of these parts will cause the output voltage to rise.

The fuse is normal and has no output voltage

The fuse is normal, and the absence of output voltage indicates that the switching power supply is not working or has entered a protective state. The first step is to check the value of the starting voltage of the starting pin of the power control chip, if there is no starting voltage or the starting voltage is too low, then check whether the external components and starting resistance of the starting pin are leakage.

If the power control chip is normal, the fault can be quickly found through the above monitoring. If there is a starting voltage, then measure whether there is a jump of high and low level at the output end of the control chip at the moment of start-up, 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, and the control chip is replaced, the peripheral components are checked, and they are checked one by one; If it is in the case of jumping, most of the cases are due to poor or damaged switches.

The insurance burns out or blows up

Mainly inspect the rectifier bridge, each diode, switch tube and the large filter capacitor on 300 volts. It may also be caused by problems in the anti-interference circuit. In particular, it is worth noting that the fuse burns due to the breakdown of the switch tube, which usually burns out the power control chip and the current sense resistor. Thermistors are also susceptible to burnout along with the insurance