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Old 6th August 2007, 11:29 PM   #1
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Red face 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.
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Old 6th August 2007, 11:53 PM   #2
AKN is offline AKN  Sweden
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Default 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.
I hope quasi doesn't hear you.
Take a look at the schematics here
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Old 6th August 2007, 11:53 PM   #3
Eva is offline Eva  Spain
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Do some research about quasi-complementary class-AB amplifiers
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Old 7th August 2007, 12:23 AM   #4
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Thanks, so this is called quasi-complementary.

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.
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Old 7th August 2007, 12:45 AM   #5
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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...
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Old 7th August 2007, 02:33 AM   #6
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Thank you Eva, it all makes sense now.
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