Diagnosis and maintenance measures when encountering abnormal voltage output of switching power supply
1. Maintenance skills for switching power supply voltage without output
The fault diagnosis method and steps
The primary task of this type of troubleshooting is to determine whether the fault is in the collector of the switch, the base of the switch or the switch. The specific method is to measure the collector and base voltage of the switch tube. There are several possible situations:
(1) The collector voltage of the switching tube is 0v, which is 1.4 times lower than that of the mains. The switch tube has no normal working voltage. If the voltage is 1.4 times, it means that the working voltage of the collector of the switching tube is normal, and it means that the AC220V and the rectification and filtering circuit are working normally.
(2) The base voltage of the switch tube is 0V (including the start-up moment). This indicates that the starting circuit does not provide the starting (conducting) voltage to the base of the switch tube, or the related components between the base and the emitter are damaged, and the starting circuit, the emitter of the switch tube and related components should be checked. If the voltage is between 0.6 and 0.7 (including the moment of power-on), it indicates that the start-up circuit, emitter and components of the switch are normal. When the voltage is higher than 0.7V, it indicates that the start-up circuit is normal, but the emitter junction of the switch tube or its components are open circuit or resistance The value increases.
(3) The switch tube has the conduction condition: the base voltage of the switch tube is 0.6~0.7V, and the collector voltage is greater than 250V, which means that the switch tube has working conditions. The fault occurs in the positive feedback circuit, including positive feedback resistors, capacitors, freewheeling diodes, and positive feedback windings of switching transformers and the connection plates between them.
Second, switching power supply momentary voltage output maintenance skills
(1) Dummy load method
(2) Measure whether the protection element is damaged
(3) Disconnection method
(4) Step-down method. The first point has to mention the strong load capacity of Minrong switching power supply, which can be said to be based on safety and pursuit. It can be said that Minrong switching power supply has the advantages of high efficiency, high safety, low loss, etc., which are inseparable from strong contributions. Similarly, the high-quality load capacity of Minrong switching power supply is inseparable from Minrong Electric's adherence to safety and pursuit of users.
Each functional circuit step-down detection method. After judging which part of the switching power supply is faulty through the above methods, the inspection methods for each part are as follows:
(1) Check the pulse width modulation circuit and positive feedback circuit. There are two ways to replace the electrolytic capacitor in the positive feedback circuit of the current switching power supply, one is 0.016UF0.039uf The failure rate of the capacitor is very low and can be eliminated through inspection. The other is an electrolytic capacitor around 10uF. This capacitor can be replaced directly during an overhaul.
(2) In the absence of an AC voltage regulator, for overvoltage protection faults, for safety reasons, you can first replace the vulnerable parts in the circuit formed by the working voltage of the pulse width modulation circuit, that is, the filter capacitor (from a few microfarads to 100uF electrolytic capacitor) to see if the switching power supply returns to normal.
3. Maintenance skills for low output voltage of switching power supply
The method and steps of the fault diagnosis
(1) Fault diagnosis by measuring the collector voltage of the output tube
(2) Measure the voltage of each output terminal of the switching power supply to judge the fault.
(3) The output voltage drop is larger than the column, and some output voltage drop is smaller than the column
