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References: <635074543.20161125135600@chriswilson.tv>
From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Fri, 25 Nov 2016 14:08:57 +0000
Message-ID: <CAA8k23RTESnyrPJZpPWo38J_7Mdw+bOQVeiJ+Py8O7q7kwMGug@mail.gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: H Bridge power MOSFET based amps question
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Quite simple.    Same number of FETs for given power, you either parallel
them in half-bridge,  or use singly in H bridge

But H-bridge give you four times the impedance, and high Z is always good
news, easier to work with, even if it does mean a higher value L in the
tank.

My 320V (DC) design, of course, had a high load resistance to start with at
that voltage, so half-bridge was quite adequate.   Still working fine after
nearly 20 years http://www.g4jnt.com/137tx.pdf

Andy  G4JNT

On 25 November 2016 at 13:56, Chris Wilson <chris@chriswilson.tv> wrote:

> 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
>
>
>
> --
>
>
> Best regards,
>  Chris  2E0ILY                           mailto:chris@chriswilson.tv
>
>
>
>

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<div dir=3D"ltr">Quite simple. =C2=A0 =C2=A0Same number of FETs for given p=
ower, you either parallel them in half-bridge, =C2=A0or use singly in H bri=
dge<div><br></div><div>But H-bridge give you four times the impedance, and =
high Z is always good news, easier to work with, even if it does mean a hig=
her value L in the tank.</div><div><br></div><div>My 320V (DC) design, of c=
ourse, had a high load resistance to start with at that voltage, so half-br=
idge was quite adequate. =C2=A0 Still working fine after nearly 20 years=C2=
=A0<a href=3D"http://www.g4jnt.com/137tx.pdf">http://www.g4jnt.com/137tx.pd=
f</a></div><div><br></div><div>Andy =C2=A0G4JNT</div></div><div class=3D"gm=
ail_extra"><br><div class=3D"gmail_quote">On 25 November 2016 at 13:56, Chr=
is Wilson <span dir=3D"ltr">&lt;<a href=3D"mailto:chris@chriswilson.tv" tar=
get=3D"_blank">chris@chriswilson.tv</a>&gt;</span> wrote:<br><blockquote cl=
ass=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;p=
adding-left:1ex">25 November 2016<br>
<br>
<br>
I have built a 1kW Class D amp for none linear digital transmissions<br>
around 136kHz.<br>
<br>
My Dave Pick designed amp uses four MOSFETS, two in parallel each side<br>
driven by a dedicated driver chip. I see the odd LF amp design using<br>
what&#39;s described as a H Bridge MOSFET array. The one I most recall<br>
most, by Andy Talbot used rectified 240 volt single phase mains to run<br>
it. My question is why use an H Bridge rather than paralleling more<br>
MOSFETS in what to me is a more conventional format? Does it overcome<br>
voltage or current limitations? Is it due to adding more capacitance<br>
with paralleled devices? Or does it allow a linear amp to be built?<br>
<br>
I realize a meaningful reply might be quite lengthy, so I assure you I<br>
have Googled it, but most stuff related to in the articles is<br>
industrial motor control.<br>
<br>
Secondly, in a Class D none linear amp, how is the gate resistor value<br>
chosen, and is there ever a case for not using one at all?<br>
<br>
Thirdly, am I alone in thinking the terms Drain and Source seem back<br>
to front and the names would intuitively be reversed so a Drain was<br>
called a Source and vice versa? :)<br>
<br>
Thanks. 2E0ILY<br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br>
<br>
<br>
--<br>
<br>
<br>
Best regards,<br>
=C2=A0Chris=C2=A0 2E0ILY=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0mailto:<a href=3D"mailto:ch=
ris@chriswilson.tv">chris@chriswilson.tv</a><br>
<br>
<br>
<br>
</font></span></blockquote></div><br></div>

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