Socket power failure troubleshooting usually uses the d […]
Socket power failure troubleshooting usually uses the direct observation method and process maintenance method. The following introduces maintenance methods in combination with several circuit failure phenomena.
Malfunctions in the socket power supply are almost all kinds. The most common faults are: no output voltage, no voltage regulation or poor regulation, no voltage transformation, excessive output ripple, spikes in the output switch, conducted EMI, and step changes in the input voltage or load V0 = Vs etc. in the oscillation and polarity inversion converter.
1. Maintenance method without output voltage
There is no output voltage in the DC-DC converter. There may be various reasons. You should immediately check whether it is overloaded to turn off and reduce the load to restart the power. If it still fails to start, check the rectifier power on the converter feed line. Burned out or shorted filter capacitor. If there is no problem with the unregulated power supply, check whether the power switch is short-circuited or the base has lost the driving voltage. If the base loses the driving voltage, the feedback signal may be too large. The soft start is at a low level. The chip may be damaged, or the output filter capacitor is shorted.
At this time, the feedback loop should be disconnected, and an appropriate voltage or signal should be added at the disconnection to isolate the fault.
For push-pull converters, monitor several switching cycles after power-on to check whether the transformer is saturated. If within a few cycles, the duty cycle changes due to the transistor, or the pulse cannot be coupled to the transformer, the transformer core moves along the BH curve and enters a saturated state. This inspection is usually performed after replacing the failed transistor. Any imbalance in the work cycle must be corrected. Replaced power diodes and switches must match existing components.
2. Unstable maintenance method
If the power supply has an output and the power switch works normally, but the output voltage changes with the load and input voltage, the voltage regulation effect has been lost, because the feedback signal is abnormal, or the duty cycle IC is faulty.