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-   -   Noob question about output MOSFETS (http://www.diyaudio.com/forums/class-d/106473-noob-question-about-output-mosfets.html)

theAnonymous1 6th August 2007 10:29 PM

Noob question about output MOSFETS
 
I was just wondering how the high power Tripath amps I have seen all use N-channel devices for both rails? Any class-a/b amp I have seen requires both N-channel and P-channel.:confused:

AKN 6th August 2007 10:53 PM

Re: Noob question about output MOSFETS
 
Hi,

Quote:

Originally posted by theAnonymous1
Any class-a/b amp I have seen requires both N-channel and P-channel.:confused:
I hope quasi doesn't hear you. ;)
Take a look at the schematics here

Eva 6th August 2007 10:53 PM

Do some research about quasi-complementary class-AB amplifiers ;)

theAnonymous1 6th August 2007 11:23 PM

Thanks, so this is called quasi-complementary.:o

So my next question; why did Tripath choose quasi-complementary? Is there a benefit other than only needing to stock N-channel devices? I assume N-channel gives more options with better specs too.

Eva 6th August 2007 11:45 PM

In comparison with P-ch, N-ch MOSFETs feature much lower on-resistance (Rds-on) given the same amount of silicon and the same capacitances. Rds-on is not so important in class AB because output devices operate in the linear region, but in class D they are either fully turned on or fully turned off, so Rds-on is one of the key parameters that determine how hot the thing is going to operate... ;)

theAnonymous1 7th August 2007 01:33 AM

Thank you Eva, it all makes sense now.:D


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