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Old 13th February 2006, 09:37 AM   #1
tomi is offline tomi  Wales
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Default Power transistors for Switching Amplifiers

Hi All,
I hope I'm not asking a question that's allready been answered elsewhere on this forum, but can anyone recomend power transistors for use in Class D amplifier output stages?

They would need to be rated to switch around 200v at 10A, with switching speeeds of at least 15kHz (for bass-only application) but ideally 100 to 200kHz. I'm looking for completmentary types - ie, a P-channel device and an N-channel device of similar characteristics.

MOSFETS would seem the obvious choice, but having looked inside some not-so-old switching power supplies, NPN BJTs seem to be favoured - so possibly either would do for this application?

So if anyone can recomend part numbers, books, articles on the web, data sheets or application notes I'd be very grateful.

The amplifiers, by the way, are destinned for a small (about 1kW) PA system which will be tri-amped font-of-house and have full-range amps to drive monitors. I'm currently working on other aspects of the system, so I'm affraid that there won't be any progress reports regarding amplifiers very soon.
Still, I'd appreciate any help...

Thanks
TOMi.
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Old 13th February 2006, 11:20 AM   #2
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If you want the amp to put out 1kW, then it's not a small amplifier! At these levels you'll not find suitable N and P channel power MOSFET parts, so the usual way is to use N-channel output devices, driven by something like an International Rectifier IR2110 chip, or by a discrete transistor driver. Have a look at the many 'home grown UCD' threads on here for plenty of information about this.

Don't even think of using bipolar transistors for the output stage, they'll need huge amounts of base drive current and you'll still have problems turning them on and off fast enough.
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Old 14th February 2006, 01:02 PM   #3
tomi is offline tomi  Wales
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Thanks.
Sounds like what I expected. I'm not intending to 1kW out of a single amp though - more likely an absolute maximum of 500W per amp for a 1kW total outout for the system.
You've confirmed what I suspected, that P channel FETS are not available in the same power classes as the N channel devices. I'll go back over some of the threads here, and look at the datasheet for the IC.

Cheers!
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Old 18th February 2006, 08:32 PM   #4
fredos is offline fredos  Canada
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Go this thread for complimentary P-N chanel mosfet, I just put my design for 600W 4 Ohms chanel power amp. It's full range, so you can down the switching frequency, but output coil should be bigger! I use a pair of IRF640 and 9640...

Have a nice days!

Fredos

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Yet another version of IR audio amp ??
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Old 20th February 2006, 12:35 PM   #5
tomi is offline tomi  Wales
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Ahh.. thanks again.
I'll look at this when I have more time (ie, when not at work!)
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Old 27th February 2006, 05:36 PM   #6
tomi is offline tomi  Wales
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Thanks Fredos,
That's very much the kind of circuit I had in mind - now at least I know it's a realistic proposition, and have some idea about what devices might be suitable.

Cheers
TOMi.
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Old 1st March 2006, 12:59 AM   #7
fredos is offline fredos  Canada
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That's a pleasure to help you!

Fredos

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