source:power supply Popular:adapter release time:2021-07-22 11:04:25 Article author:sznbone
The importance of switching power supply is self-evident, but once a problem occurs, it is difficult to solve. What is the reason why the switching power supply has no voltage output?
1. The reason why the switching power supply always has no voltage output
(1) The collector of the switch tube does not get enough working voltage
(2) The base of the switch tube does not get the starting voltage and the related circuit leakage
(3) The positive feedback element of the switch tube fails
2. Methods and steps to judge the fault
The first task of repairing this type of fault is to determine which of the above three parts is the drum barrier. The specific method is to measure the collector base voltage of the switch tube. There may be the following situations:
(1) The collector voltage of the switch tube is 0V and is lower than 1.4 times of the mains. The switch tube has no normal working voltage. If there is a voltage of 1.4 times, it means that the collector of the switch tube has a normal working voltage, indicating that the circuit is working normally.
(2) The base voltage of the switch tube is 0V (including the moment of power-on). This indicates that the starting circuit does not provide a starting (turn-on) voltage to the base of the switch tube, or the breakdown of related components between the base and the emitter should be checked. Starting circuit and switch tube emitter and related components. If the voltage is 0.6~0.7 (including a few moments when it is turned on), it means the starting circuit and switch tube emitter components are normal. If it is above 0.7V, it means the starting circuit is normal but the switching tube emitter junction or component is normal. Open circuit or increase in resistance.
(3) The switching tube has the conduction conditions: the base voltage of the switching tube is 0.6~0.7V, and the collector voltage is greater than 250V, indicating that the switching tube has the working conditions, and the fault lies in the positive feedback circuit, including the positive feedback resistor, capacitor, freewheeling diode and the switch The positive feedback windings of the transformer and the connections between them should be made of plates.
The reason why the switching power supply has no voltage output is introduced here, I hope it can help everyone!
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