Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mk01.r1000.mx.aol.com (Internet Inbound) with ESMTP id 41904380000D1; Tue, 9 Apr 2013 13:36:24 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1UPbww-0000Sn-L0 for rs_out_1@blacksheep.org; Tue, 09 Apr 2013 18:03:14 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1UPbwv-0000Se-Td for rsgb_lf_group@blacksheep.org; Tue, 09 Apr 2013 18:03:13 +0100 Received: from mout0.freenet.de ([195.4.92.90]) by relay1.thorcom.net with esmtps (UNKNOWN:AES256-GCM-SHA384:256) (Exim 4.77) (envelope-from ) id 1UPbwt-0004WM-Ja for rsgb_lf_group@blacksheep.org; Tue, 09 Apr 2013 18:03:12 +0100 Received: from [195.4.92.140] (helo=mjail0.freenet.de) by mout0.freenet.de with esmtpa (ID dl4yhf@freenet.de) (port 25) (Exim 4.80.1 #2) id 1UPbwY-0008P8-Fi for rsgb_lf_group@blacksheep.org; Tue, 09 Apr 2013 19:02:50 +0200 Received: from localhost ([::1]:57689 helo=mjail0.freenet.de) by mjail0.freenet.de with esmtpa (ID dl4yhf@freenet.de) (Exim 4.80.1 #2) id 1UPbwY-00007V-3z for rsgb_lf_group@blacksheep.org; Tue, 09 Apr 2013 19:02:50 +0200 Received: from [195.4.92.18] (port=54328 helo=8.mx.freenet.de) by mjail0.freenet.de with esmtpa (ID dl4yhf@freenet.de) (Exim 4.80.1 #2) id 1UPbtu-0005QE-G6 for rsgb_lf_group@blacksheep.org; Tue, 09 Apr 2013 19:00:06 +0200 Received: from blfd-d9bf2bc1.pool.mediaways.net ([217.191.43.193]:4628 helo=[192.168.178.22]) by 8.mx.freenet.de with esmtpsa (ID dl4yhf@freenet.de) (TLSv1:DHE-RSA-CAMELLIA256-SHA:256) (port 465) (Exim 4.80.1 #2) id 1UPbtt-00047h-Lg for rsgb_lf_group@blacksheep.org; Tue, 09 Apr 2013 19:00:06 +0200 Message-ID: <51644914.8080900@freenet.de> Date: Tue, 09 Apr 2013 19:00:04 +0200 From: wolf_dl4yhf User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:14.0) Gecko/20120713 Thunderbird/14.0 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <7EB77D10460A4EBF9E1F63437A4C99A6@gnat> <5163262C.60204@freenet.de> In-Reply-To: X-Spam-Score: -2.4 (--) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Hi Alan, Of course when the reed switch closes, it must not (never, ever) directly switch the drain current ! (To do that, one would need an "opener" which are quite exotic devices for reed switches, with built-in permanent magnets). [...] Content analysis details: (-2.4 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [195.4.92.90 listed in list.dnswl.org] 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (dl4yhf[at]freenet.de) -2.4 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message X-Scan-Signature: b2d5972cffc09bc55071138bfa4f6e53 Subject: Re: LF: Re: Hall Effect for Over-current shutdown? Content-Type: multipart/alternative; boundary="------------080704020207050009000403" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.6 required=5.0 tests=HTML_20_30, HTML_FONTCOLOR_UNSAFE,HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G x-aol-sid: 3039ac1d61855164519746ad X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. --------------080704020207050009000403 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Hi Alan, Of course when the reed switch closes, it must not (never, ever) directly switch the drain current ! (To do that, one would need an "opener" which are quite exotic devices for reed switches, with built-in permanent magnets). What I would use the reed switch for is to 'remove the driving signal', or kill the FET's drain voltage. To break the drain current (if the FET had died), one would need another -separate- MOSFET of course, which would then operate like an electronic fuse. Use a flipflop with reset-input to enable the supply voltage after the protection circuit has tripped. Or add some more elaborate control circuitry which doesn't cut off the drain supply voltage completely; instead reduce it to a level at which the FET withstands even the worst output mismatch. This would allow tuning (at low power), and then, after the SWR is ok, reset the flipflop to switch back to "normal" (high) power. All the best, Wolf . 08.04.2013 23:01, schrieb Alan Melia: > Hi Wolf I cant remember the ratings now but breaking 18A+ might be a > bit cruel :-)) It would probably need more than a tap with a pencil > to unstick it ! > Alan > G3NYK > > ----- Original Message ----- > *From:* wolf_dl4yhf > *To:* rsgb_lf_group@blacksheep.org > > *Sent:* Monday, April 08, 2013 9:18 PM > *Subject:* Re: LF: Re: Hall Effect for Over-current shutdown? > > .. 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 >> *To:* rsgb_lf_group >> *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 >> > > 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 >> *To:* rsgb_lf_group >> >> *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 >> > --------------080704020207050009000403 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit
Hi Alan,

Of course when the reed switch closes, it must not (never, ever) directly switch the drain current !
(To do that, one would need an "opener" which are quite exotic devices for reed switches, with built-in permanent magnets).

What I would use the reed switch for is to 'remove the driving signal', or kill the FET's drain voltage.
To break the drain current (if the FET had died), one would need another -separate- MOSFET of course, which would then operate like an electronic fuse. Use a flipflop with reset-input to enable the supply voltage after the protection circuit has tripped. Or add some more elaborate control circuitry which doesn't cut off the drain supply voltage completely; instead reduce it to a level at which the FET withstands even the worst output mismatch. This would allow tuning (at low power), and then, after the SWR is ok, reset the flipflop to switch back to "normal" (high) power.

All the best,
  Wolf .

08.04.2013 23:01, schrieb Alan Melia:
Hi Wolf I cant remember the ratings now but breaking 18A+ might be a bit cruel :-))  It would probably need more than a tap with a pencil to unstick it !
 
Alan
G3NYK
 
----- Original Message -----
Sent: Monday, April 08, 2013 9:18 PM
Subject: Re: LF: Re: Hall Effect for Over-current shutdown?

.. 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 -----
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> 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 -----
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

 


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