Why does LED light during Withstand Voltage Test?

1. Generation mechanism

When hi-pod voltage is applied between input and FG, electric charges pass through ground capacitor C2 and C3, and electrifies C1. And if the voltage charged on C1 reaches to the start-up voltage of switching power supply, switching circuit (TR1,OT) will operate and then output voltage will be generated. However, there are only a few electric charges charged on C1, so switching circuit will shut off immediately.

The above process will be repeated since voltage is applied, and pulse-shape voltage will occur on the output. As long as the circuit is operated under control, there is no probability that output voltage will rise and exceed the rated voltage. In addition, there is no influence for the reliability of power supply because there is no abnormal voltage occurring on the internal components of power supply.

Fig.1 Circuit diagram of the inside of a power supply

2. Safety of output load equipment

We consider there is no impact on the load equipment because the output voltage will not exceed the rated voltage. However, in case if some countermeasures are required due to the characteristics of the equipment, make a short circuit between the output terminals during the test.

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