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Date: Fri, 25 Nov 2016 15:07:56 +0100
From: DK7FC <selberdenken@posteo.de>
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References: <635074543.20161125135600@chriswilson.tv>
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Subject: Re: LF: H Bridge power MOSFET based amps question
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Hi Chris,

A H bridge can handle the 320V DC much easier. It is a question of the 
availability of high voltage rated MOSFETs. In a H bridge you can use 
normal 500V types, like the cheap IRFP460A. For the design you chose you 
will need 1000V FETs. They are available nowadays. So just try it if you 
like :-)

I never used gate resistors in front of my FETs. Oh, no, thats wrong. I 
used 1 Ohm resistors to flatten the oscillation that appears on the L to 
H edge. But this was in the H bridge only where i have to use gate 
transformers. For hard switched FETs you don't need them (even if others 
tell you to you do!) :-)

73, Stefan

Am 25.11.2016 14:56, schrieb Chris Wilson:
> 25 November 2016
>
>
> I have built a 1kW Class D amp for none linear digital transmissions
> around 136kHz.
>
> My Dave Pick designed amp uses four MOSFETS, two in parallel each side
> driven by a dedicated driver chip. I see the odd LF amp design using
> what's described as a H Bridge MOSFET array. The one I most recall
> most, by Andy Talbot used rectified 240 volt single phase mains to run
> it. My question is why use an H Bridge rather than paralleling more
> MOSFETS in what to me is a more conventional format? Does it overcome
> voltage or current limitations? Is it due to adding more capacitance
> with paralleled devices? Or does it allow a linear amp to be built?
>
> I realize a meaningful reply might be quite lengthy, so I assure you I
> have Googled it, but most stuff related to in the articles is
> industrial motor control.
>
> Secondly, in a Class D none linear amp, how is the gate resistor value
> chosen, and is there ever a case for not using one at all?
>
> Thirdly, am I alone in thinking the terms Drain and Source seem back
> to front and the names would intuitively be reversed so a Drain was
> called a Source and vice versa? :)
>
> Thanks. 2E0ILY
>
>
>
>