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Old 24th June 2004, 12:16 PM   #51
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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.
Don't forget the forward voltage of the "freewheeling diodes".

Regards

Charles
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Old 24th June 2004, 12:23 PM   #52
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Hi,

Yeah I deleted those,

Regards
Chris
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Old 24th June 2004, 12:45 PM   #53
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Quote:
Originally posted by Eva
I've got performances as good as 50ns or less charge/discharge times for an IRFP460 switching 300V [including 'miller' capacitance effects, very noticeable at these high voltages]
Hey eva, you should have a play with a Fairchild IRFP460A. We use then at work very often. Unbelievable performance for a bread-and-butter mosfet. They also claim a turnoff time of 6nS.
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Old 24th June 2004, 07:39 PM   #54
Pafi is offline Pafi  Hungary
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Hi, Chris!

"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."

Yes, it indicates the natural "pumping". The current converted to voltage on Rds.

"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."

I don't understand this.


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

IR2110. BTW: I use IGBTs because supply voltage is over +/-100V.

To avoid cross-conduction, slow down gate charging.
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Old 29th June 2004, 11:09 AM   #55
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Hi Pafi,

Well with bad DC offset the output power would look uneven, 600watt peak....200 watt peak......600........200....etc

Yeh, I figured out what needs to be done to fix it (cross conduction) but instead of doing that I'm working on a different driver circuit altogether for it.

Regards,
Chris
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