Radio Amateur Quiz Canadian License

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Question A-004-002-011

In a properly designed choke input filter power supply, the no-load voltage across the filter capacitor will be about nine-tenths of the AC RMS voltage yet it is advisable to use capacitors rated at the peak transformer voltage. Why is this large safety margin suggested?

Correct Answer

Under no-load conditions and a burned-out bleeder, voltages could reach the peak transformer voltage

Explanation

If the bleeder resistor (which provides minimum load) fails in a choke-input supply, and there's no external load, the filter can behave more like a capacitor-input filter, allowing the output voltage to rise towards the peak AC voltage.

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