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Common Problems and Solutions of Power Adapters

Ⅰ. The circuit problem of the power adapter


Line problems, including damage to the power cord and no electricity, poor contact of the DC head, etc. Focus on checking whether the input line and output line can be powered on normally.


If the Chinese power adapter line is faulty, it can be solved by replacing the DC line or AC line.


Ⅱ. The output voltage of the power adapter is too low


The following are the main reasons for low output voltage:


1. Power supply load short-circuit fault (especially DC/DC converter short-circuit or poor performance, etc.), first disconnect all loads of the 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. The failure of the filter capacitor or rectifier diode at the output voltage end can be judged by the replacement method.


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.


4. The poor switching transformer will not only cause the output voltage to drop, but also cause insufficient excitation of the switch tube and damage the switch tube.


5. The 300V filter capacitor is not good, resulting in poor load capacity of the power supply, and the output voltage will drop as soon as the load is connected.


Ⅲ. The output voltage of the power adapter is too high


The output voltage is too high generally from the voltage regulator sampling and voltage regulator control circuit. 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.


Ⅳ. The fuse of the power adapter is normal, and there is 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 startup voltage of the startup pin of the power control chip. If there is no startup voltage or the startup voltage is too low, check whether the components connected to the startup pin and the startup resistor are leaking.


If the power control chip is normal, the fault can be quickly found through the above detection. If there is a start-up voltage, measure whether the output terminal of the control chip has high and low level jumps at the moment of power-on. 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. Check one by one by replacing the control chip and checking the peripheral components; if there is a jump, in most cases, the switch tube is bad or damaged.


5. The fuse of the power adapter is burned out or blown up


Mainly check the rectifier bridge, diodes, switch tubes and large filter capacitors on 300 volts. It may cause the fuse to burn and become black, or it may be caused by a problem with the anti-jamming circuit.


It is especially worth noting that the fuse is burned due to the breakdown of the switch tube, which usually burns out the power control chip and the current detection resistor. The thermistor is also easy to burn out along with the fuse.

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