Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id wAUEw91q029806 for ; Fri, 30 Nov 2018 15:58:10 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gSk8E-0002Ag-UX for rs_out_1@blacksheep.org; Fri, 30 Nov 2018 14:51:02 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gSk81-0002AM-09 for rsgb_lf_group@blacksheep.org; Fri, 30 Nov 2018 14:50:49 +0000 Received: from smtpq3.tb.ukmail.iss.as9143.net ([212.54.57.98]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91_59-0488984) (envelope-from ) id 1gSk7y-0004SG-Nb for rsgb_lf_group@blacksheep.org; Fri, 30 Nov 2018 14:50:47 +0000 Received: from [212.54.57.80] (helo=smtp1.tb.ukmail.iss.as9143.net) by smtpq3.tb.ukmail.iss.as9143.net with esmtp (Exim 4.86_2) (envelope-from ) id 1gSk7x-0008JN-AX for rsgb_lf_group@blacksheep.org; Fri, 30 Nov 2018 15:50:45 +0100 Received: from oxbe17.tb.ukmail.iss.as9143.net ([172.25.160.148]) by smtp1.tb.ukmail.iss.as9143.net with ESMTP id Sk7xgkSIViA02Sk7xgrIF8; Fri, 30 Nov 2018 15:50:45 +0100 X-DKIM-Result: Domain=virginmedia.com Result=Signature OK X-Env-Mailfrom: daveyxm@virginmedia.com X-Env-Rcptto: rsgb_lf_group@blacksheep.org X-SourceIP: 172.25.160.148 X-CNFS-Analysis: v=2.3 cv=bp4y+3Si c=1 sm=1 tr=0 a=C4ceZvFKwZ2eZ1YMZ8iQeA==:117 a=FufuyOdfgJMA:10 a=j3Jg0PKBWEQA:10 a=79bTZUIPAAAA:8 a=gDAFGJbyAAAA:8 a=QejfARXMAAAA:8 a=ebku8kW9l4MamBRWk9IA:9 a=QEXdDO2ut3YA:10 a=a7NF8HQaSwMA:10 a=x9bLkTXwpMUA:10 a=VK3FegllBdDeeq2MVgUA:9 a=di19p-zDfz_F8fPX:21 a=_W_S_7VecoQA:10 a=ISTIEq08UyDe2sYTrcO4:22 a=H2WkEZGh68wRIEKhhMIM:22 a=BC3gsuZa1vz2YJYxs7Nf:22 X-Authenticated-Sender: daveyxm@virginmedia.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=virginmedia.com; s=meg.feb2017; t=1543589445; bh=7CwgZVemTXuWffDN664X0oB290EKfrn/4yqmwXeiB3c=; h=Date:From:To:In-Reply-To:References:Subject; b=JwgBuR8c15zfXzNIxkTINqSoF7TaH1VHcfrcQ1A1/H1jHVh6iTP06sp8pDCG781QL MJqvbfwcdXI69G9t578ovtjSABBWHR3NO9A+XHnOnQo0HuZzCNnnaArcG6DDOpVktE lUa+SsuxwWNxR1rlFdchZrNPeyPyrTVZUXLkyy8k1LXpiLVuMQSEm+EEAJaR0LmmQJ /GkRU6uAGsTlT5gGzUoZo66rKpYR9+NDYps3tRaCxjfcrh3bg2hrEAQ4SaUANSjfb3 Z8t/TIqG7z4lKxGdUWwIIQzVr4ekWkU2bb3Hgb/FcwEgZKae3LDwtONBOIv1auLpxi dbjOqvoIqe2/g== Date: Fri, 30 Nov 2018 14:50:45 +0000 (GMT) From: DAVE PICK To: paul@n1bug.com, "Discussion of the Lowfer (US, European, & UK) and MedFer bands" , rsgb_lf_group@blacksheep.org Message-ID: <1382885588.67051.1543589445229@mail2.virginmedia.com> In-Reply-To: <27270b29-dde1-1207-1158-becc1e4de123@n1bug.com> References: <2133457080.64533.1543584595217@mail2.virginmedia.com> <27270b29-dde1-1207-1158-becc1e4de123@n1bug.com> MIME-Version: 1.0 X-Priority: 3 Importance: Medium X-Mailer: Open-Xchange Mailer v7.8.4-Rev47 X-Originating-IP: 92.233.158.110 X-Originating-Client: open-xchange-appsuite X-CMAE-Envelope: MS4wfJWTKkV++nrzemK7NNBnLRJ9H9nVGdlCUiyECl6ekk/CAwA7UQGcL6u76WxhaJKh/1cOohPpY0ImRjBSslCYyLVSs0JJ9E7T8RI1zvNSepA788jUahqK KSMWCfiPk96BxRFE7JYlg24tBUxYwjHW+Uym8bisKhatzQdb44c4ti8rIHmntPl7c3ICfBLVQNPL9EMnvxeC73YZs3J+d5cA1dBqORjIHrk5dJDbDzDMT0ys 1z5u6PGruXQU5EBT9PFobJQ7YM7GQHgiHAYyJRS94u0= X-Spam-Score: -0.7 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: Paul If you look at the spec sheets most of these FETs have a large input (gate) capacitance. Some are more than 5000pF. This is taking the clean edges off your drive waveform. The FQA34N20 was only 2450pF [...] Content analysis details: (-0.7 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.7 RCVD_IN_DNSWL_LOW RBL: Sender listed at http://www.dnswl.org/, low trust [212.54.57.98 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: c1dcf088149efa0360827745859da381 Subject: Re: [Lowfer] LF: Re: FET change, hmmm Content-Type: multipart/alternative; boundary="----=_Part_67050_760989466.1543589445224" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=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 ------=_Part_67050_760989466.1543589445224 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Paul If you look at the spec sheets most of these FETs have a large input (gate) capacitance. Some are more than 5000pF. This is taking the clean edges off your drive waveform. The FQA34N20 was only 2450pF, so a good choice. The IRFP260 is at 4000pF, mid way. Seems you have to spend serious money to get the low-capacitance FETs! Dave > On 30 November 2018 at 14:36 N1BUG wrote: > > > Thanks Dave! > > Your note prompted me to go back to the bench and look at this > again. I think I just might be starting to get a clue. I'm not the > brightest but I really am making an effort to learn. > > I made some more tests with the oscilloscope. > > Looking at the output of the IR2110 FET driver *without* FETs > connected, the rise and fall slopes are extremely steep with a > clear, flat dead zone between the end of the fall on one side and > start of rise on the other. > > With FETs connected but no Vdd, the slopes are far less steep and > the fall just reaches zero as the rise on the other side begins. > (with the original FETs there was still a flat dead zone here) > > Applying minimal Vdd (13V), the slopes become less steep again plus > they have large FET turn-on / turn-off "steps" along the rise / > fall slopes. Now the falling side has not reached zero as the rising > side is starting up. > > I don't know how much of this is due to the speed of the FETs and > how much may be softening of the rise / fall due to lead inductance > or other phenomena in my gate circuit / driver board as more current > is sourced / sinked. But I do know the slopes with these FETs are > not as steep as with the previous FETs. > > It should be quite interesting to install faster FETs and do these > checks again. > > 73, > Paul > > > > On 11/30/18 8:29 AM, DAVE PICK wrote: > > > > Paul > > > > Try the Infineon IRFP260MPBF they are fast and reasonably priced. > > I use Ixys IXFH58N20 but they are expensive... they are the best > > though! Can't find any FQA34N20 over here from reputable > > sources. > > > > Dave G3YXM > > > > > > > On 30 November 2018 at 12:58 N1BUG > > mailto:paul@n1bug.com mailto:paul@n1bug.com > wrote: > > > > > > > > > Yesterday I replaced FETs in my 2200 meter amplifier. Since > > > the FQA34N20 is long discontinued I had no choice but to make > > > a substitute. I chose the FQA32N20C because I know of one > > > active station using them in the same amplifier with success. > > > > > > I notice drain ringing is significantly greater with the new > > > FETs, but maybe acceptable. I have little choice but to run the > > > amp and see how it goes. > > > > > > I also notice the gate voltage decay takes about twice as long > > > as the old FETs. According to the data sheets, turn off fall > > > time on the 32N20C is almost twice that of the 34N20. I suppose > > > that is what I am seeing. I *guess* this may be related to > > > increased ringing, as it appears one side is not fully off as > > > the other begins to switch on. > > > > > > I would appreciate any comments or suggestions, including > > > suggestions for a FET which might leave a longer dead zone at > > > the phase transition. I'd think slow to turn on, fast to turn > > > off would be nice... > > > > > > Alternatively, if anyone has a stash of FQA34N20 purchased from > > > a well respected vendor (old stock) and would be willing to > > > sell some, I may be interested. I've already tried some which > > > originated from a Chinese source and am not interested in going > > > down that road again. :-) > > > > > > 73, Paul N1BUG > > > > > > > > > > > ______________________________________________________________ > Lowfer mailing list > Home: http://mailman.qth.net/mailman/listinfo/lowfer > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Lowfer@mailman.qth.net mailto:Lowfer@mailman.qth.net > Post must be less than 50KB total for message plus attachment! > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ------=_Part_67050_760989466.1543589445224 MIME-Version: 1.0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Paul

If you look at the spec sheets most of these FETs = have a large input (gate) capacitance. Some are more than 5000pF.
This i= s taking the clean edges off your drive waveform.
The FQA34N20 was only = 2450pF, so a good choice.
The IRFP260 is at 4000pF, mid way. Seems you h= ave to spend serious money to get the low-capacitance FETs!

Dave
=
On 30 November 2018 at 14:36 N1BUG <paul@n1bug.com> wrote:


Thanks= Dave!

Your note prompted me to go back to the bench and look at thi= s
again. I think I just might be starting to get a clue. I'm not the=
brightest but I really am making an effort to learn.

I made some= more tests with the oscilloscope.

Looking at the output of the IR21= 10 FET driver *without* FETs
connected, the rise and fall slopes are ext= remely steep with a
clear, flat dead zone between the end of the fall on= one side and
start of rise on the other.

With FETs connected but= no Vdd, the slopes are far less steep and
the fall just reaches zero as= the rise on the other side begins.
(with the original FETs there was st= ill a flat dead zone here)

Applying minimal Vdd (13V), the slopes be= come less steep again plus
they have large FET turn-on / turn-off "s= teps" along the rise /
fall slopes. Now the falling side has not rea= ched zero as the rising
side is starting up.

I don't know how= much of this is due to the speed of the FETs and
how much may be soften= ing of the rise / fall due to lead inductance
or other phenomena in my g= ate circuit / driver board as more current
is sourced / sinked. But I do= know the slopes with these FETs are
not as steep as with the previous F= ETs.

It should be quite interesting to install faster FETs and do th= ese
checks again.

73,
Paul



On 11/30/18 8:29 AM,= DAVE PICK wrote:
Paul

Try the Infineon IRF= P260MPBF they are fast and reasonably priced.
I use Ixys IXFH58N20 but t= hey are expensive... they are the best
though! Can't find any FQA34N= 20 over here from reputable
sources.

Dave G3YXM
On 30 November 2018 at 12:58 N1BUG <paul@n1bug.com
mailto:pau= l@n1bug.com > wrote:


Yesterday I replaced FETs in my 220= 0 meter amplifier. Since
the FQA34N20 is long discontinued I had no choi= ce but to make
a substitute. I chose the FQA32N20C because I know of one=
active station using them in the same amplifier with success.

I = notice drain ringing is significantly greater with the new
FETs, but may= be acceptable. I have little choice but to run the
amp and see how it go= es.

I also notice the gate voltage decay takes about twice as longas the old FETs. According to the data sheets, turn off fall
time on t= he 32N20C is almost twice that of the 34N20. I suppose
that is what I am= seeing. I *guess* this may be related to
increased ringing, as it appea= rs one side is not fully off as
the other begins to switch on.

I = would appreciate any comments or suggestions, including
suggestions for= a FET which might leave a longer dead zone at
the phase transition. I&#= 39;d think slow to turn on, fast to turn
off would be nice...

Alt= ernatively, if anyone has a stash of FQA34N20 purchased from
a well resp= ected vendor (old stock) and would be willing to
sell some, I may be int= erested. I've already tried some which
originated from a Chinese sou= rce and am not interested in going
down that road again. :-)

73, = Paul N1BUG
______________________________________= ________________________
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Help: http://ma= ilman.qth.net/mmfaq.htm
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This list hosted by: http://www.qsl.net
P= lease help support this email list: http://www.qsl.net/donate.html =20 ------=_Part_67050_760989466.1543589445224--