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Old 16th June 2004, 03:05 PM   #41
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Here is the odd power offset
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Old 16th June 2004, 03:07 PM   #42
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Full circuit
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Old 16th June 2004, 04:21 PM   #43
Eva is offline Eva  Spain
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I'm just curious...

To what MOSFETs are you comparing those IGBTs?
What rise/fall times or waveforms are you getting from the MOSFETs?

My experience is the opposite since replacing two IRFP460 [from ST] by two SKP10N60 [from Infineon] reduced total losses somewhat in a single-phase 160-240V AC to 450V DC 2000W PFC simple home-made prototype, specially at full load, and ugly 10-30Mhz RF ringing was no longer present at switching transients

PD: I'm using a coupled inductor plus saturable reactor combination to delay the current rise about 100nS [giving the switches enough time to saturate] and then ramp-up the current on the switches at 50A/us in order to avoid dissipation during diode reverse recovery [stored energy on this inductor is dumped back to the output at turn-off and next cycle is delayed if it starts when the inductor is still discharging]. This method reduces dramatically switching losses but the 'saturable core' quickly overheats since I actually have no access to saturable reactor cores and I'm using standard ferrite materials with high losses for that purpose
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Old 16th June 2004, 07:05 PM   #44
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Hi,

well...I have the dc offset solved.... how does -40mV sound? nnnnnnot bad I think, part of the problem actually was pspice..Otherwise I would have found it much sooner.

Curiously the PWM output still has what looks like supply pumping that hasnt' changed much at all. Should I care?

I find my highest levels of distortion with this circuit occur with low inputs.. 1W output for instance is the worst...while 500Watts out has the last distortion. Is that spice playing a game with me?

Chris
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Old 23rd June 2004, 04:53 PM   #45
Pafi is offline Pafi  Hungary
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Hi Chris!

Don't simulate, build it! :-)

I built it yesterday (same principle, but different realising), and it work perfectly! Author is right: it's the ultimate (SE) classD!

"the PWM output still has what looks like supply pumping"

What do you mean?

Thank you for the link again!
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Old 23rd June 2004, 05:06 PM   #46
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Quote:
Curiously the PWM output still has what looks like supply pumping that hasnt' changed much at all. Should I care?
How much ?`

Regards

Charles
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Old 23rd June 2004, 05:58 PM   #47
Pafi is offline Pafi  Hungary
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How can be seen supply pumping on output?
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Old 24th June 2004, 06:46 AM   #48
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Quote:
How can be seen supply pumping on output?
I was wondering about this also at first. Then I came to the conclusion that he may be talking about the PWM signal as such, i.e. BEFORE the output filter.
There you will see it of course, simply because you switch between the two rails.

Regards

Charles
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Old 24th June 2004, 07:23 AM   #49
Pafi is offline Pafi  Hungary
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Thanks! You must be right!
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Old 24th June 2004, 12:56 PM   #50
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Hi,

Yes, I have about a 1 volt of ripple on the pwm output, which is the inverse of the input signal and carries through out the system.

The DC offset would cause the ripple to be far worse on alternate wave peaks and also affect the output voltage. With the dc offset minimally optimised it carries through just over a 1/4 volt.

Pafi, If I built it i'd be having +-200amps cross conduction right now. What was your implementation of the mosfet driver?
Chris
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