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Old 15th December 2008, 06:23 PM   #11
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Whoa, I was wrong.

A 2Hz sine was able to drive the rail voltage to almost 90V without the over-current protection tripping.

It fried the 150V MOSFETs I had put in. They were working fine with the normal 73V tail voltage, even with a continuous 20Hz sine at almost full volume.

So this is a real problem, even with unregulated supplies. I don't think it is that big of a concern normally as no one in their right mind would let their woofers oscillate at ~2Hz, let alone at any significant volume.
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Old 15th December 2008, 08:58 PM   #12
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Modify the amplifier, use the low frequency cutoff points from the various coupling capacitors to prevent excessive rail pumping.

Try to find a 200V replacement MOSFET with a fast body diode and low charges, even if it comes in another package, for example IRFB4227.

Paralleling more devices is likely to cause trouble due to the gate charge increase.
I use to feel like the small child in The Emperor's New Clothes tale
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Old 16th December 2008, 02:57 AM   #13
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I have already decided to go with the IRFP4227PBF.
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