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Old 24th December 2004, 07:13 AM   #1
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Default protecting high-powered mosfet amplifiers..

Hi there.

I have an existing mosfet amplifier design, and I would like to add some current protection to the design. Can anyone point me to a page or 2 where I can learn more about how to do this?

Also, I would like to know abit more about adding more power transistors in parallel. Is it always a simple case of just adding a couple more of them in parallel, each with their own gate driving resistor?

In the case of adding more power transistors to a current-limited bipolar design, how do I go about that? I have seen designs where the current through one of the pairs is measured and this signal is used for current limiting purposes, while the rest of the pairs only have each their own emitter resistor. Is this the way to go?

Why do the current limiting transistors always have a diode and a resistor from their base to the output? The resistor I understand, forms part of a voltage devider to set the current limiting point. Is the diode there to "enable" the current limiting of each side only during it's active cycle?

Many question I have asked. I now leave it to the masters of audio to come and educate the layperson..

regards
Carel
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Old 24th December 2004, 09:06 AM   #2
mikeks is offline mikeks  United Kingdom
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send me mail...
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Old 1st January 2005, 05:06 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
Is anyone willing to give us a short paper on protecting FET output power amps?
regards Andrew T.
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Old 1st January 2005, 05:31 PM   #4
sam9 is offline sam9  United States
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Try this link for an example of a multislope protection circuit. http://www.sealelectronics.com/kits/images/OPTI1001.pdf

You probably have to use different values with different output components and topology but the idea remains the same. \


You can also look at the zener + GP diode in ESP's Project 101. This is pretty much straight from the Exicon app-note (or other sources) This is allegedly too slow if you use double-die MOSFETS and I've read that while it protects the devices, when it activates it may (will?) blow the rail fuses.
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Old 3rd January 2005, 05:26 AM   #5
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Hi there

Michael Kiwanuka emailed me a brilliant paper he wrote about VI limiting protection. It has great detail and is a must-read to all amplifier guys.

He has given me permission to forward this to other people, so drop me an email at carel(AT)pteq.net and I will pas it on.

regards
Carel
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Old 3rd January 2005, 05:42 AM   #6
Electrons are yellow and more is better!
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I got this paper also from Mike (did you remembr this?), very well written. Why can't you be equally clear when you post here? Anyway, this paper would do the trick for amp_man!
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Old 3rd January 2005, 06:57 AM   #7
sajti is offline sajti  Hungary
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Yes. It would be great if You can put up to this forum!

sajti
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Old 5th January 2005, 08:07 AM   #8
Did it Himself
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I already have the paper from Mike and will host it on my webspace if Mike says that's OK.
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Old 5th January 2005, 09:17 AM   #9
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by richie00boy
I already have the paper from Mike and will host it on my webspace if Mike says that's OK.
Please don't host it on ANY webspace.....as i don't OWN copyright.....Cheers.
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Old 5th January 2005, 09:29 AM   #10
Electrons are yellow and more is better!
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... but aren't you the author? Have you written this document for somebody else and given up the copyright?
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