Customizable Switching Power Supplies With Factory Price

Common Failures of Switching Power Supplies

Burn fuse: this phenomenon is a more serious phenomenon in the switching power supply, resulting in fuse burning, mainly to check whether the ends of the 400V filter capacitor short-circuit phenomenon, rectifier bridge and each diode whether there is a breakdown phenomenon, there is also a problem with the EMI line can also lead to fuse meltdown, if the fuse burned, then we first need to measure the current-limiting resistor whether there is a burned open-circuit, followed by the measurement of the MOS tube whether breakdown, the chip surface whether there is obvious burned out phenomenon. Measure whether the MOS tube is broken, whether the chip surface has obvious burnt phenomenon, generally fuse will be accompanied by NTC negative temperature thermistor, rectifier bridge together with the damage, so the replacement should pay attention to a one-time replacement of the complete, otherwise there will be repeated melting phenomenon.

Fuse is normal, but the product has no output: first of all, we have to measure whether the high voltage DC is normal, and then measure whether there is voltage at the start-up pin of the power control chip, if there is no start-up voltage or the start-up voltage is too low to cause the failure to start, then we have to check the start-up resistor and the start-up pin of the external wiring whether there is a problem, if there is a start-up voltage, then the next measurement is whether there is a high and low level of the control chip's output in the power-on moment. Jump, if there is no jump, then the control chip is bad, or peripheral circuit components or protection line problems, we generally if the naked eye can not see the problems such as even tin solder, then replace a chip, and then check the peripheral components, if the chip has a voltage jump, then the next step should be to measure the switching tube gate whether there is a voltage to start, if there is a voltage to start then, then the problem Generally appear in the transformer or the secondary side of the output circuit.

Output, but the output voltage is too high: this fault generally comes from the voltage sampling and voltage control circuit; in the DC output, sampling resistor, error sampling amplifier TL431, optocoupler, power supply chip and other devices constitute a closed control loop, any one of the problems will lead to increased output voltage.

Low output voltage: low output voltage in addition to voltage regulator circuit problems will lead to low output voltage, there are several other possibilities, such as power supply load there is a short-circuit phenomenon, at this time a more effective way is to disconnect the load to see whether the power supply output is normal, there is also a diode at the output side or the filter capacitor failure, will also trigger the low output voltage phenomenon; switching tube performance degradation, which will lead to the power supply Switching tube performance degradation will lead to power supply internal resistance increases, the ability to carry load decreases, the output voltage is low; transformer windings are not the right number, or core problems, etc. will lead to low voltage; there is a relatively rare is the 400V filter capacitor is bad, which will cause the power supply to reduce the ability to carry load, the output voltage will drop linearly as soon as a load is connected.

We have also encountered a relatively rare phenomenon, that is, no-load energized, the measurement of voltage is normal, but placed 30S after the switch will burn out, troubleshooting for a long time without great progress, and finally with the help of a thermal imager, and finally found that the switch tube burned out due to the temperature has been rising caused by the measurement of the RCD absorber line of resistance resistance, resulting in excessive current, the diode is in the soft breakdown state, resulting in the switching of the diode. After measurement, it was found that the resistance in the RCD absorber line became blocked, resulting in too much current, and the diode was in a soft breakdown state, which led to the breakdown of the switch.

If you want to know more about switching power supply information, you can consult Xiamen Eahunt Electronics.

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Email: athene-cai@eahunt.com

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