source:Industry News Popular:adapter release time:2021-12-28 10:17:21 Article author:sznbone
The following are the main reasons for the low output voltage caused by the power adapter:
1. Switching power supply load short-circuit failure (especially DC/DC converter short-circuit or poor performance, etc.), at this time, first disconnect all loads of the switching 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 it is still abnormal, it means that the switching power supply circuit is faulty.
2. The failure of the filter capacitor or rectifier diode at the output voltage can be judged by the replacement method.
3. The performance of the switching tube is degraded, causing the switching tube to fail to conduct normally, which increases the internal resistance of the power supply and reduces the load capacity.
4. Poor switching transformer not only causes the output voltage to drop, but also causes insufficient excitation of the switching tube and damages the switching tube.
5. The poor 300V filter capacitor results in poor load carrying 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 voltage generally comes from voltage stabilization sampling and voltage stabilization control circuits. In the closed control loop composed of DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, any one of the components will cause the output voltage to rise.
The fuse is normal, 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 external components of 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 monitoring. If there is a startup voltage, measure whether there are high and low level jumps at the output terminal of the control chip 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, and the control chip is replaced. Chips, check the peripheral components, and check them one by one; if they are changing, most of them are bad or damaged switch tubes.
Insurance burned out or blown up
Mainly check the rectifier bridge, each diode, switch tube and the large filter capacitor on 300 volts and other parts. It may cause the insurance to burn and turn black, or it may be caused by a problem with the anti-interference circuit. It is especially worth noting that the fuse is burnt 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 insurance
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