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What is the power factor of a classical power supply ? I mean a transformer, rectifier and filter capacitor. Is it constant ?

Marus Gradinaru
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    This depends on the size of the decoupling capacitor and that one depends on the amount of ripple which is acceptable. – Janka May 02 '17 at 21:57
  • I measured a PF for a classical PSU and when loaded I read PF around 0.4...0.6 – G36 May 02 '17 at 22:07

2 Answers2

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There is no one answer. No, it is not constant.

Think about it. When there is no load on the output, the transformer primary just looks like a inductor. However, when there is a load there are current spike twice per line cycle when the rectifiers conduct. That adds a lot of harmonics, which contribute to a lower power factor.

Olin Lathrop
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When a bridge rectifier is used you get a very non-linear current taken from the AC supply because the diodes are only conducting for a small duration of the time: -

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This can make the overall power factor very poor but it is load dependent and this means there is no one fixed value for power factor.

Andy aka
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