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Old 10th September 2010, 11:18 PM   #1
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Default Excellent tutorial on Class AB MOSFET output stage design!

I found this while Googling ; whilst this application note is titled regarding a National Op-Amp part - the application note has voluminous detail on selecting MOSFET outputs, biasing, distortion and other design constraints.

National AN-1645 Application Note

-- Jim
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Old 11th September 2010, 06:56 AM   #2
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Thanks for posting this, Jim. It's certainly an informative AN. and a great find.
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Old 11th September 2010, 08:00 AM   #3
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National semi is a great resource. They sell CHIPS and to get the most out of them good reference circuits are needed. I heeded this app note....
http://www.national.com/an/AN/AN-1849.pdf

Not only a lot of good advice on the devices themselves , but a reference board with all the "tricks" to get .000 X %THD from their product.
The mosfet app note is valuable , but I must find one that has the reference board also.
OS
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Old 11th September 2010, 01:01 PM   #4
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Quote:
Originally Posted by jrdmedford View Post
I found this while Googling ; whilst this application note is titled regarding a National Op-Amp part - the application note has voluminous detail on selecting MOSFET outputs, biasing, distortion and other design constraints.

National AN-1645 Application Note

-- Jim
LM4702 Driving a MOSFET Output Stage.
I had seen it before, and it is great reading!

One funny thing.
One titel for part conerning slew rate is:
SLOW RATE

This is what can call the slew rate in a very SLOW Amplifier
What slow rate has your bad amp?
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Old 11th September 2010, 02:42 PM   #5
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Quote:
Originally Posted by jrdmedford View Post
I found this while Googling ; whilst this application note is titled regarding a National Op-Amp part - the application note has voluminous detail on selecting MOSFET outputs, biasing, distortion and other design constraints.

National AN-1645 Application Note

-- Jim
This is definitely a good app note that I have seen before. Among other things, it deals with the amount of bias spreading voltage that is available for the MOSFETs, where the amount allowed by this part may not be sufficient for some MOSFETs with high Vgs. For MOSFETs with higher Vgs, the LME49830 is a good choice. I cover these considerations in a chapter in my new book, "Designing Audio Power Amplifiers". I also have a whole chapter devoted to MOSFET power amplifiers. As many of you know, I like MOSFET output stages.

Cheers,
Bob
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