Question on PFC front ends for SMPS

The common flyback PWM can't output current to the AC line, so can't accurately fake a capacitance or inductance. Their positive peak current could be shifted in time, which would technically be a power factor shift.

Other circuits could, given adequate reservoir capacitance, really sim an L or C over the whole cycle.

John

You can take the line in through an inductor and chop it with a bridge (so it looks like you're driving the line with the bridge's output), and operate with PWM in a current loop so that the line current is always proportional to the line voltage, or some phase shift thereof. This is scaled by the DC error voltage on the output rail, so the voltage remains regulated while 120Hz ripple (or 360Hz if you do this with a three phase chopper for industrial use) appears on the filter cap.

You're basically running a VFD in reverse. Two of these, back to back, would do a great job running motors; unsurprisingly, this is often done.

Tim

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"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Darn. I guess that approach won't work then. Thanks for the info.