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 wAUFnQLf030022 for ; Fri, 30 Nov 2018 16:49:37 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gSkrp-0002Pj-1R for rs_out_1@blacksheep.org; Fri, 30 Nov 2018 15:38:09 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gSkrV-0002Pa-5C for rsgb_lf_group@blacksheep.org; Fri, 30 Nov 2018 15:37:49 +0000 Received: from mail-ed1-x531.google.com ([2a00:1450:4864:20::531]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91_59-0488984) (envelope-from ) id 1gSkrR-0004ZR-8K for rsgb_lf_group@blacksheep.org; Fri, 30 Nov 2018 15:37:48 +0000 Received: by mail-ed1-x531.google.com with SMTP id r27so5213480eda.0 for ; Fri, 30 Nov 2018 07:37:43 -0800 (PST) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=kSOFATmrVTIc5N1SZAV+CZ5GyjCUzdpugHR0E2h0NwU=; b=fk1BORWTbvWL2vWlwp7vermOMqHjGExN4mg3FPdNC+0LApEL2RqDEcNgwg7Sows5ds tfx9uOjkfCmHojWK3FXmtApCU3clWO0ckr8phlUMQHboDpXA9NKRgRBQTtwP8ErlY1Kj eI24+T7Y+kJpITWUmj+XSaXFqszHNlJ6YnC8Im9d+/oQRu3IjJOIS0XxbwNimRjXNW5R PSbgHe5fvYFoTqq/FuIuKA48BEmxxG9k42eBl0tc1VTkMAhmcVVWrBU++mENzPmF4hDV f7NC2nSNEsWie1j4AOor0UUlTumHgF8Fidf7PVWN5ymx3/s7sb1CAHWIz4Cq0pC9OgV+ DKVg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=kSOFATmrVTIc5N1SZAV+CZ5GyjCUzdpugHR0E2h0NwU=; b=F8tNGdaisA/O8pIbj1X2oEzlNO3KyqyCK4K5EoQZuSoLggLMEVR3snUcznrtQcOgkf OHq5wGjWKnZHF4UdZb9+dLNo5o5eMlA8g4hwLCu9+xATwmlrqhcEhbk9ShQ70AffDqsQ 1kXxMBAycK7PL5XEePhLSZmuc4g2L2sLej4y5M6Hl3eK1+OvwKQH3GbYldhmEAlBpQfs 0QLGNz1ioXRkJCMzWh9p0tTJYJhf7Zn/GU5RIbvUQgK5LrOg91u4k9jcE6TY3XrhUG1i sPm2GXpjwnBABHN+vxdfOAebJcYRfo90p7PamnHr7pYH3uZ1dU+DtRB9p8P30Czo2ysp WpNw== X-Gm-Message-State: AA+aEWZZWQg7r87sTznumKebh3d+7acmJhrul6NGi8Er57wwigJYGYoZ 60d0Cmx3lxxntVGaRjkC5GdJZgTAvooc7ASCwlAusQ== X-Google-Smtp-Source: AFSGD/WQFOePXnZ1TTWo3KVdF+pe4UkmnI6KtvouI0Pg6zAjKPsjE6ci6kKOXvTn80o+0bp1l3i567wP2ifOe2lhCoI= X-Received: by 2002:a17:906:c7c9:: with SMTP id dc9-v6mr4940151ejb.232.1543592262309; Fri, 30 Nov 2018 07:37:42 -0800 (PST) MIME-Version: 1.0 References: <2133457080.64533.1543584595217@mail2.virginmedia.com> <27270b29-dde1-1207-1158-becc1e4de123@n1bug.com> <1382885588.67051.1543589445229@mail2.virginmedia.com> <530677a9-52b1-0280-128f-4afc58f94536@n1bug.com> In-Reply-To: <530677a9-52b1-0280-128f-4afc58f94536@n1bug.com> From: Andy Talbot Date: Fri, 30 Nov 2018 15:37:31 +0000 Message-ID: To: "rsgb_lf_group@blacksheep.org" Cc: lowfer@mailman.qth.net X-Spam-Score: 0.0 (/) 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: Millar feedback capacitance The multiplication of Gate-Drain capacitance due to negative feedback. Don't just look at Cgs, but also at Cgd Andy www.g4jnt.com Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [2a00:1450:4864:20:0:0:0:531 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (andy.g4jnt[at]gmail.com) 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: f548c2e6c4e712c1eb3dcc8bf83f0d4f Subject: Re: [Lowfer] LF: Re: FET change, hmmm Content-Type: multipart/alternative; boundary="000000000000791cc0057be394d6" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_20_30,HTML_MESSAGE, TO_ADDRESS_EQ_REAL 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 --000000000000791cc0057be394d6 Content-Type: text/plain; charset="UTF-8" Millar feedback capacitance The multiplication of Gate-Drain capacitance due to negative feedback. Don't just look at Cgs, but also at Cgd Andy www.g4jnt.com On Fri, 30 Nov 2018 at 15:12, N1BUG wrote: > Understood but there has got to be more to it that my mind is not > absorbing. The FQA32N20C spec sheet gives 1700 pf but they are > making the waveform much softer than the FQA34N20's spec'd at 2400 > pf did. What am I missing here? > > 73, > Paul > > > On 11/30/18 9:50 AM, DAVE PICK wrote: > > 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 >> mailto:paul@n1bug.com > 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 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 > > --000000000000791cc0057be394d6 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Millar feedback capacitance

<= /div>
The multiplication of Gate-Drain capacitance=C2=A0 due to ne= gative feedback.=C2=A0 =C2=A0 Don't just look at Cgs,=C2=A0 but also at= Cgd


=
Andy

<= /div>

=

On Fri, 30 Nov 2018 a= t 15:12, N1BUG <paul@n1bug.com>= wrote:
Understood but there has go= t to be more to it that my mind is not
absorbing. The FQA32N20C spec sheet gives 1700 pf but they are
making the waveform much softer than the FQA34N20's spec'd at 2400<= br> pf did. What am I missing here?

73,
Paul


On 11/30/18 9:50 AM, DAVE PICK wrote:
> 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 <paul@n1bug.com
>> mailto:paul@n1= bug.com > 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" alon= g 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<= br> >> 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 fro= m
>>> reputable sources.
>>>
>>> Dave G3YXM
>>>
>>>>>> On 30 November 2018 at 12:58 N1BUG <paul@n1bug.com
>>>>>> mailto:paul@n1bug.com
>>>> 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 bu= t
>>>> to make a substitute. I chose the FQA32N20C because I know=
>>>> of one active station using them in the same amplifier wit= h
>>>> success.
>>>>
>>>> I notice drain ringing is significantly greater with the >>>> new FETs, but maybe acceptable. I have little choice but t= o
>>>> run the amp and see how it goes.
>>>>
>>>> I also notice the gate voltage decay takes about twice as<= br> >>>> 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<= br> >>>> may be related to increased ringing, as it appears one sid= e
>>>> 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, fa= st 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 alread= y
>>>> tried some which originated from a Chinese source and am >>>> not interested in going down that road again. :-)
>>>>
>>>> 73, Paul N1BUG

--000000000000791cc0057be394d6--