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Power adapter common failures and troubleshooting methods

by:Fuyuang     2020-05-21
Line fault, including the power cord damage not electricity, contact oxidation poor contact, and so on and so forth. Key check whether the input line and output line is electricity. If the line fault, can be solved by changing the way such as the power cord. The following is the main reason for the low output voltage, switching power supply load short circuit fault (1 Short circuit or poor performance especially in DC/DC converter, etc. ) , at this point, first disconnect all the load switch power supply circuit, checking is switch power supply circuit failure or malfunction with the load circuit. If you disconnect the load circuit and voltage output is that is under the heavy load; Or is still not normal of switch power supply circuit fault. 2 output voltage terminal filter or rectifier diode failure, etc. , can be determine by replacing method. 3 switch tube performance degradation, leading to switch tube can't normal conduction, increase the resistance of power supply, load ability. 4 switch transformer is bad, not only cause the loss of output voltage, at the same time cause the switch tube insufficient incentives to damage the switch tube 5 300 v filter capacitance is bad, causes the power load ability is poor, a load output voltage will drop. Generally comes from the high voltage output voltage sampling and voltage control circuit. In the dc output resistance, sampling, sampling error amplifier such as TL431, optical coupling, the power control chip circuit constitute closed loop control, any one parts problems are leading to higher output voltage. Insurance tube is normal, no output voltage switching power supply does not work or go into a state protection. The first step is to check the power supply control chip start feet start voltage value, without start voltage or start voltage is too low, then check whether start foot external components and start the resistance leakage. If the power supply control chip is normal, can quickly via the monitoring to the malfunction. If a start-up voltage, then measuring the output of the control chip in the boot instantly whether there is a high and low level of the jump, if not jump, that control chip damage, damage to the peripheral oscillation circuit element, or failure protection circuit, by replacing the control chip, check the peripheral components, check one by one; If the jump, most of the time for the switch tube bad or damaged. Mainly check the rectifier bridge, diode, switch tube and 300 v on the filter capacitor etc. Cause insurance burning, black, also may be anti-interference circuit caused this problem. Particularly notable is: insurance burn caused by switch tube breakdown, often burn out power control chip and current sense resistor. Thermistors are also easy to burn the power supply control with insurance.
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