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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Sun, 8 Apr 2018 13:09:42 +0100
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To: LineOne <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: W1VD amp help
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In my half-bridge 700 Watt design, http://www.g4jnt.com/137tx.pdf  I used a
small inductor between the top and bottom FETs to absorb the energy from
any short glitch when both devices are on.   In a transformer push-pull
like that I'm not sure how you'd implement exactly that idea, but a small L
in each drain may suffice.   Saves having to complicate the drive waveform
with a deliberately induced dead zone.

Andy  G4JNT

On 8 April 2018 at 12:53, N1BUG <paul@n1bug.com> wrote:

> Jay,
>
> Thanks for the detailed response! See below, threaded in.
>
> > HP3325A ... set frequency x2, square wave, amplitude 5 volts, dc
> > offset 2.5 volts. Have used the HP3325A here for countless numbers
> > of years.
>
> Done, verified that it looks OK with scope. (Previously I had not
> been testing with the DC offset!)
>
> > Always start out on the dummy load.
>
> I've reduced drain voltage to 13V so that I can do that. I have no
> dummy load which can handle the next step up (25V). No one near me
> does either.
>
> > Test in stages. Test the driver
> > into the FETs with the FET drain supply off. Verify the waveforms
> > with a dual trace scope to see that there's a small 'dead zone'
> > between the two phases.
>
> There is a delay between one phase beginning to switch off and the
> other phase beginning to switch on, but I am not sure I would quite
> call it a 'dead zone'.
>
> Sorry about the quality of images. Scope 5V/div.
>
> Gate waveforms:
>
> http://www.n1bug.com/gates1.jpg
>
> With the traces overlaid and time stretched out so you can better
> see the crossing between phases:
>
> http://www.n1bug.com/gates2.jpg
>
> It appears one has not fallen to zero by the time the other one is
> coming up. Should it?
>
> > Once the gate waveforms are confirmed to be correct,
>
> I've paused testing at this point pending any comment on my gate
> waveforms or request to repeat with different settings.
>
> Paul
>
>

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<div dir=3D"ltr">In my half-bridge 700 Watt design,=C2=A0<a href=3D"http://=
www.g4jnt.com/137tx.pdf">http://www.g4jnt.com/137tx.pdf</a>=C2=A0 I used a =
small inductor between the top and bottom FETs to absorb the energy from an=
y short glitch when both devices are on.=C2=A0 =C2=A0In a transformer push-=
pull like that I&#39;m not sure how you&#39;d implement exactly that idea, =
but a small L in each drain may suffice.=C2=A0 =C2=A0Saves having to compli=
cate the drive waveform with a deliberately induced dead zone.<div><br></di=
v><div>Andy=C2=A0 G4JNT</div></div><div class=3D"gmail_extra"><br><div clas=
s=3D"gmail_quote">On 8 April 2018 at 12:53, N1BUG <span dir=3D"ltr">&lt;<a =
href=3D"mailto:paul@n1bug.com" target=3D"_blank">paul@n1bug.com</a>&gt;</sp=
an> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;=
border-left:1px #ccc solid;padding-left:1ex">Jay,<br>
<br>
Thanks for the detailed response! See below, threaded in.<br>
<span class=3D""><br>
&gt; HP3325A ... set frequency x2, square wave, amplitude 5 volts, dc<br>
&gt; offset 2.5 volts.=C2=A0Have used the HP3325A here for countless=C2=A0n=
umbers<br>
&gt; of years.<br>
<br>
</span>Done, verified that it looks OK with scope. (Previously I had not<br=
>
been testing with the DC offset!)<br>
<span class=3D"">=C2=A0=C2=A0<br>
&gt; Always start out on the dummy load.<br>
<br>
</span>I&#39;ve reduced drain voltage to 13V so that I can do that. I have =
no<br>
dummy load which can handle the next step up (25V). No one near me<br>
does either.<br>
<span class=3D""><br>
&gt; Test in stages.=C2=A0Test the driver<br>
&gt; into the FETs with the FET drain supply off. Verify the waveforms<br>
&gt; with a dual trace scope to see that there&#39;s=C2=A0a small=C2=A0&#39=
;dead zone&#39;<br>
&gt; between the two phases.<br>
<br>
</span>There is a delay between one phase beginning to switch off and the<b=
r>
other phase beginning to switch on, but I am not sure I would quite<br>
call it a &#39;dead zone&#39;.<br>
<br>
Sorry about the quality of images. Scope 5V/div.<br>
<br>
Gate waveforms:<br>
<br>
<a href=3D"http://www.n1bug.com/gates1.jpg" rel=3D"noreferrer" target=3D"_b=
lank">http://www.n1bug.com/gates1.<wbr>jpg</a><br>
<br>
With the traces overlaid and time stretched out so you can better<br>
see the crossing between phases:<br>
<br>
<a href=3D"http://www.n1bug.com/gates2.jpg" rel=3D"noreferrer" target=3D"_b=
lank">http://www.n1bug.com/gates2.<wbr>jpg</a><br>
<br>
It appears one has not fallen to zero by the time the other one is<br>
coming up. Should it?<br>
<span class=3D""><br>
&gt; Once the gate waveforms are=C2=A0confirmed=C2=A0to be correct,<br>
<br>
</span>I&#39;ve paused testing at this point pending any comment on my gate=
<br>
waveforms or request to repeat with different settings.<br>
<br>
Paul<br>
<br>
</blockquote></div><br></div>

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