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Date: Tue, 09 Apr 2013 18:46:20 +0200
From: wolf_dl4yhf <dl4yhf@freenet.de>
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Content preview: Hi Warren, Indeed it requires a few milliseconds (the small
reed relay contacts can switch at one or two hundred Hertz) but you don't
need to shut off the MOSFET within a few thousand cycles of the carrier frequency
- the FET will have to tolerate short pulses of overcurrent anyway. [...]
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Subject: Re: LF: Re: Hall Effect for Over-current shutdown?
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Hi Warren,
Indeed it requires a few milliseconds (the small reed relay contacts can
switch at one or two hundred Hertz) but you don't need to shut off the
MOSFET within a few thousand cycles of the carrier frequency - the FET
will have to tolerate short pulses of overcurrent anyway.
All the best,
Wolf .
Am 09.04.2013 17:02, schrieb Warren Ziegler:
> Wolf, interesting idea, but doesn't contact closure take about 10ms?
>
> 73 Warren
>
>
>
> On Mon, Apr 8, 2013 at 4:18 PM, wolf_dl4yhf <dl4yhf@freenet.de
> <mailto:dl4yhf@freenet.de>> wrote:
>
> .. or wind a few turns of fat copper wire around a 'reed relay'
> contact tube. Virtually no voltage loss then. I used this for a
> power supply, but it would work for the DC current feed inside a
> PA as well. IIRC, the product of number of turns * Amperes was
> about 50 for the contact to close.
>
> 73,
> Wolf .
>
> Am 08.04.2013 21:39, schrieb Alan Melia:
>> Ah yes that is Class D and can go that way if
>> mis-matched......that is a lot of power in a sensing resistor! I
>> guess a Hall effect device or even a temp sensor would do that
>> job. I think in over current condition a lot of power is
>> dissipated in the devices. High side sensors should be available
>> at 30v The sheets I have seen, suggest they require some
>> assistance above about 40v.
>> Alan
>>
>> ----- Original Message -----
>> *From:* Warren Ziegler <mailto:wd2xgj@gmail.com>
>> *To:* rsgb_lf_group <mailto:rsgb_lf_group@blacksheep.org>
>> *Sent:* Monday, April 08, 2013 8:07 PM
>> *Subject:* Re: LF: Re: Hall Effect for Over-current shutdown?
>>
>> Hi Alan,
>>
>> I've modified the G0MRF amp with the M0BMU output
>> configuration, I'm using a 30V supply.
>> The G0MRF uses a current sense resistor to shut down the amp
>> quickly in case too much current is being draw.
>> I've modified the output transformer turns ratio to produce
>> more power at lower supply voltages (I'm using 500V, 55a FETs).
>> However with the new higher currents and with a new
>> appropriate value sense resistor its developing a LOT of heat
>> (12 W or so) and needs to be heat-sinked.
>> I'm thinking Hall-effect might be more efficient and produce
>> less heat - I'm pretty sure that others have used Hall effect
>> devices to protect MOSFET amplifier and I'm looking for
>> circuit tips.
>>
>> 73 & Tnx!
>> Warren
>>
>>
>>
>>
>> On Mon, Apr 8, 2013 at 2:52 PM, Alan Melia
>> <alan.melia@btinternet.com
>> <mailto:alan.melia@btinternet.com>> wrote:
>>
>> Ah interesting problem Warren.... why is it
>> over-current?? if it is over-current because a high
>> voltage has welded/melted a short between drain and
>> source, then the protection wont help ....high currents
>> usually lead to excess heating ......but what is the real
>> cause? If you really need DC supply protection would not
>> a high-side current monitor be easier/faster??? The
>> problem then could be there is enough energy stored in
>> the PA choke to zap the FET before, or even if, you can
>> disconnect the supply.
>> OK drive fails permanently on might be a condition it
>> would protect the FETs against with DC coupled drive
>> Alan G3NYK
>>
>> ----- Original Message -----
>> *From:* Warren Ziegler <mailto:wd2xgj@gmail.com>
>> *To:* rsgb_lf_group
>> <mailto:rsgb_lf_group@blacksheep.org>
>> *Sent:* Monday, April 08, 2013 7:15 PM
>> *Subject:* LF: Hall Effect for Over-current shutdown?
>>
>> Anyone using a Hall effect device for overcurrent
>> sensing and shutdown in a MOSFET amplifer?
>>
>> --
>> 73 Warren K2ORS
>> WD2XGJ
>> WD2XSH/23
>> WE2XEB/2
>> WE2XGR/1
>>
>>
>>
>>
>> --
>> 73 Warren K2ORS
>> WD2XGJ
>> WD2XSH/23
>> WE2XEB/2
>> WE2XGR/1
>>
>
>
>
>
> --
> 73 Warren K2ORS
> WD2XGJ
> WD2XSH/23
> WE2XEB/2
> WE2XGR/1
>
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<div class="moz-cite-prefix">Hi Warren,<br>
<br>
Indeed it requires a few milliseconds (the small reed relay
contacts can switch at one or two hundred Hertz) but you don't
need to shut off the MOSFET within a few thousand cycles of the
carrier frequency - the FET will have to tolerate short pulses of
overcurrent anyway. <br>
<br>
All the best,<br>
Wolf .<br>
<br>
Am 09.04.2013 17:02, schrieb Warren Ziegler:<br>
</div>
<blockquote
cite="mid:CAMFjj72iSc6GRG+MuMtoHhsvYp0AMotZ_aOgYvwtOHzdRmKGrg@mail.gmail.com"
type="cite">
<div dir="ltr">Wolf, interesting idea, but doesn't contact closure
take about 10ms?
<div><br>
</div>
<div style="">73 Warren</div>
<div style=""><br>
</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Mon, Apr 8, 2013 at 4:18 PM,
wolf_dl4yhf <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:dl4yhf@freenet.de" target="_blank">dl4yhf@freenet.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>.. or wind a few turns of fat copper wire around a
'reed relay' contact tube. Virtually no voltage loss
then. I used this for a power supply, but it would work
for the DC current feed inside a PA as well. IIRC, the
product of number of turns * Amperes was about 50 for
the contact to close.<br>
<br>
73,<br>
Wolf .<br>
<br>
Am 08.04.2013 21:39, schrieb Alan Melia:<br>
</div>
<div>
<div class="h5">
<blockquote type="cite">
<div><font face="Arial">Ah yes that is Class D and
can go that way if mis-matched......that is a
lot of power in a sensing resistor! I guess a
Hall effect device or even a temp sensor would
do that job. I think in over current condition a
lot of power is dissipated in the devices. High
side sensors should be available at 30v The
sheets I have seen, suggest they require some
assistance above about 40v.</font></div>
<div> </div>
<div><font face="Arial">Alan</font></div>
<blockquote style="BORDER-LEFT:#000000 2px
solid;PADDING-LEFT:5px;PADDING-RIGHT:0px;MARGIN-LEFT:5px;MARGIN-RIGHT:0px"
dir="ltr">
<div style="FONT:10pt arial">----- Original
Message ----- </div>
<div style="FONT:10pt arial;BACKGROUND:#e4e4e4"><b>From:</b>
<a moz-do-not-send="true"
title="wd2xgj@gmail.com"
href="mailto:wd2xgj@gmail.com" target="_blank">Warren
Ziegler</a> </div>
<div style="FONT:10pt arial"><b>To:</b> <a
moz-do-not-send="true"
title="rsgb_lf_group@blacksheep.org"
href="mailto:rsgb_lf_group@blacksheep.org"
target="_blank">rsgb_lf_group</a> </div>
<div style="FONT:10pt arial"><b>Sent:</b> Monday,
April 08, 2013 8:07 PM</div>
<div style="FONT:10pt arial"><b>Subject:</b> Re:
LF: Re: Hall Effect for Over-current shutdown?</div>
<div><br>
</div>
<div dir="ltr">Hi Alan,
<div><br>
</div>
<div> I've modified the G0MRF amp with the
M0BMU output configuration, I'm using a 30V
supply.</div>
<div>The G0MRF uses a current sense resistor to
shut down the amp quickly in case too much
current is being draw.</div>
<div>I've modified the output transformer turns
ratio to produce more power at lower supply
voltages (I'm using 500V, 55a FETs).</div>
<div>However with the new higher currents and
with a new appropriate value sense resistor
its developing a LOT of heat (12 W or so) and
needs to be heat-sinked.</div>
<div>I'm thinking Hall-effect might be more
efficient and produce less heat - I'm pretty
sure that others have used Hall effect devices
to protect MOSFET amplifier and I'm looking
for circuit tips.</div>
<div><br>
</div>
<div>73 & Tnx!</div>
<div>Warren</div>
<div><br>
</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Mon, Apr 8, 2013 at
2:52 PM, Alan Melia <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:alan.melia@btinternet.com"
target="_blank">alan.melia@btinternet.com</a>></span>
wrote:<br>
<blockquote style="BORDER-LEFT:#ccc 1px
solid;MARGIN:0px 0px 0px
0.8ex;PADDING-LEFT:1ex" class="gmail_quote">
<div bgcolor="#ffffff">
<div><font face="Arial">Ah interesting
problem Warren.... why is it
over-current?? if it is over-current
because a high voltage has
welded/melted a short between drain
and source, then the protection wont
help ....high currents usually lead to
excess heating ......but what is the
real cause? If you really need DC
supply protection would not a
high-side current monitor be
easier/faster??? The problem then
could be there is enough energy stored
in the PA choke to zap the FET before,
or even if, you can disconnect the
supply.</font></div>
<div> </div>
<div><font face="Arial">OK drive fails
permanently on might be a condition it
would protect the FETs against with DC
coupled drive</font></div>
<div> </div>
<div><font face="Arial">Alan G3NYK</font></div>
<blockquote style="BORDER-LEFT:#000000 2px
solid;PADDING-LEFT:5px;PADDING-RIGHT:0px;MARGIN-LEFT:5px;MARGIN-RIGHT:0px"
dir="ltr">
<div style="FONT:10pt arial">-----
Original Message ----- </div>
<div style="FONT:10pt
arial;BACKGROUND:#e4e4e4"><b>From:</b>
<a moz-do-not-send="true"
title="wd2xgj@gmail.com"
href="mailto:wd2xgj@gmail.com"
target="_blank">Warren Ziegler</a> </div>
<div style="FONT:10pt arial"><b>To:</b>
<a moz-do-not-send="true"
title="rsgb_lf_group@blacksheep.org"
href="mailto:rsgb_lf_group@blacksheep.org" target="_blank">rsgb_lf_group</a>
</div>
<div style="FONT:10pt arial"><b>Sent:</b>
Monday, April 08, 2013 7:15 PM</div>
<div style="FONT:10pt arial"><b>Subject:</b>
LF: Hall Effect for Over-current
shutdown?</div>
<div><br>
</div>
<div dir="ltr">Anyone using a Hall
effect device for overcurrent sensing
and shutdown in a MOSFET amplifer?<span><font
color="#888888"><br clear="all">
<div><br>
</div>
-- <br>
73 Warren K2ORS<br>
WD2XGJ <br>
WD2XSH/23<br>
WE2XEB/2<br>
WE2XGR/1<br>
<br>
</font></span></div>
</blockquote>
</div>
</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
73 Warren K2ORS<br>
WD2XGJ <br>
WD2XSH/23<br>
WE2XEB/2<br>
WE2XGR/1<br>
<br>
</div>
</blockquote>
</blockquote>
<br>
</div>
</div>
</div>
</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
73 Warren K2ORS<br>
WD2XGJ <br>
WD2XSH/23<br>
WE2XEB/2<br>
WE2XGR/1<br>
<br>
</div>
</blockquote>
<br>
</body>
</html>
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