Noob question about output MOSFETS

[theAnonymous1]

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.

 

[AKN]

Hi,

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

 

[Eva]

Do some research about quasi-complementary class-AB amplifiers

 

[theAnonymous1]

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.

 

[Eva]

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]

Thank you Eva, it all makes sense now.