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Kevin Weddle

current and voltage out of phase

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Power supplies are usually DC and use a big filter capacitor or an inductor in series with the filter capacitor to block AC with the inductor and short the AC to ground with the capacitor to smooth the rectifier pulses. The resistance of the inductor reduces the output current available from the power supply.

DC doesn't have phase relashionships. AC signals do.

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Does current that is out of phase with voltage mean lower available power. I see inductors used everywhere in power supplies, but are they used for more than ripple reduction?



It is all about the Power Triangle. So the answer is, it depends on what you mean by power. If the current and voltage are in phase, all of the power will be "real" so real power = apparent power or KW = KVA.

If there is an inductor or a capacitor in the circuit, the voltage and current will be out of phase, therefore the real power will be the same but there will be a component of "active" power which has a phasor +/- 90 degrees out of phase with the real power. When you determine the "apparent Power" it will now be more than the "real" power or KVA>KW

The long story short is study the power triangle.

Audioguru, there are many types of AC power supplies, what about a UPS or a VFD?

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Is there any relevance to this concept? I use reactance for phase calculation, and I can't think of where the current/voltage phase relationship is ever used. I just figured that if I had a capacitor in an AC power application, I could add an inductor somewhere and get more power. Maybe that's why motors have capacitors.

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