Common faults and repairs of the power adapter

　　In our daily life, we often come into contact with the power adapter. When using it, we often encounter some problems, such as common contact failure, voltage instability or insurance burnout. How do we check and eliminate? What? The following Lefeng share the common faults and repairs of the charger/power adapter.

　　The power adapter produced by the regular manufacturer has a nameplate indicating the power, input and output voltage and current quantity. Of note is the input voltage range. In general, a charger/power adapter with an input voltage of 110V-240V is available worldwide and is suitable for all countries and regions.

　　Common faults and repairs of the power adapter:

　　First, the line is faulty

　　Line faults, including power line damage, non-energization, poor contact contact oxidation, etc. Focus on checking whether the input and output lines are powered.

　　If the line is faulty, you can solve it by replacing the power cord.

　　Second, the output voltage is too high

　　The output voltage is too high and generally comes from the regulated sampling and voltage regulation control circuit. In the closed control loop formed by 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.

　　Third, the output voltage is too low

　　The following are the main causes of low output voltage:

　　1 Switching power supply load short-circuit fault (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 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 output voltage terminal filter capacitor or rectifier diode failure, etc., 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 Switching transformer is not good, not only causes the output voltage to drop, but also causes the switching tube to be insufficiently excited to damage the switch tube.

　　The 5300V filter capacitor is poor, resulting in poor power supply load capacity, and the load output voltage will drop when connected.

　　Fourth, insurance burned or blown up

　　Mainly check the rectifier bridge, each diode, switch tube and large filter capacitors on 300 volts. This may cause the insurance to burn and blacken, or it may be caused by a problem with the anti-interference circuit.

　　In particular, it is important to note that the fuse is burnt due to the breakdown of the switch tube, which usually burns the power control chip and the current sense resistor. The thermistor is also easily burned out together with the insurance.

　　The common faults and repairs of the charger/power adapter are mentioned here. In addition, we should pay attention to the daily maintenance and maintenance of the charger/power adapter, which can reduce the occurrence of faults and effectively extend the service life.

　　Five, 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 the protection state. The first step is to check the value of the starting voltage of the start pin of the power control chip. If there is no starting voltage or the starting voltage is too low, check whether the external components of the starting pin and the starting resistor are leaking.

　　If the power control chip is normal, the fault can be quickly detected through the above monitoring. If there is a starting voltage, whether the output of the control chip has a high or low transition at the instant of power-on, if there is no jump, it indicates that the control chip is damaged, the peripheral oscillation circuit component is damaged or the protection circuit is faulty, and the replacement control is performed. Chips, check peripheral components, check one by one; if jumping, in most cases, the switch is defective or damaged.