Return to KLUBNL.PL main page

rsgb_lf_group
[Top] [All Lists]

Re: LF: Capacitor warning and First 500kHz Class E breadboard

To: [email protected]
Subject: Re: LF: Capacitor warning and First 500kHz Class E breadboard
From: Warren Ziegler <[email protected]>
Date: Mon, 10 Jan 2011 10:17:18 -0500
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=6MuFQP4PSmsq/jiENrratcDF6j66bALHRPLQRGfRMOQ=; b=hevObITf9hi52YMnky6BdwTMVZzIW8VGTjC9CDX0mkG7q52EnRrN/d2Y33JguvcGJ3 djy7K4+j1Xs/b8o3SHB1g5ETvIsWV8pxTcthyY6/XWcNrf7LMA2ymidrptvYrdmNYWfc sjD+FKg8PTDGwikPqrvA7a8SciWdgECg6K5OA=
Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=CDIUiF91vwpsPac2LknlxdGesQh+N6LCDcrE/9chnxHWRrXBM9jmQr1InI//aJeKlF s8nqc4sJ7Bk90g0akZb4aB48eo31kxtYOiqwRHyPlzbhnIUe9+gvqGUV+iWdCV1cBiy8 qR4l/k9jEJnrBVR9o8FW0zG5DFN2YS0OaOW1w=
Domainkey-status: good (testing)
In-reply-to: <[email protected]>
References: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Andy,

    hams around here use multi-layer ceramic caps for high power
class-E service, specifically the ATC series caps from American
Technical Ceramics:
http://www.atceramics.com/products/multilayer_capacitors.asp

Very stable, high current (single ATC100C will handle 12 amps), and
small in size!
-- 
73 Warren K2ORS
                WD2XGJ
                WD2XSH/23
                WE2XEB/2
                WE2XGR/1



On Mon, Jan 10, 2011 at 9:22 AM, Andy Talbot <[email protected]> wrote:
> A warning to anyone contemplating making power amps - especially class E
> types.
> Don't even think about using the small high voltage ceramic caps availalble
> at low cost from the suppliers - and sold as "suitable for SMPSUs etc"  in
> resonant circuits
> They are appalling, terrible, revolting things.  You only have to breath on
> them and they change their value.wildly
>
> These things    http://www.g4jnt.com/Download/UselessCaps.jpg
>
> I've just  made up a first version of a breadboard for a 500kHz Class E
> amplifier, (target design 500W from 50 V supply),  calculated the L/C values
> as per Alan's spreadsheet, combined with an L matched output for 50 ohm.
> For the capacitors I aimed to get within 5% of the calculated values using
> many of these small ceramic objects in parallel - lots in || should share
> the current, shouldn't they, which would be good?
>
> So I soldered them up - used the G4HUP L/C meter to measure the values - at
> which point I should have been a bit suspicious as the measured C was
> sometimes a fair bit lower than it should have been.  At the time I just put
> it down to "finger trouble" - one does tend to ignore little things like
> that sometimes.
> Anyway, made up the amp, used a 12V supply rail and monitored the switching
> waveforms, expecting to see something vaguely approaching the half sine on
> drains etc.
>
> Results, terrible, nowhere near what they should have been - clearly summat
> was very wrong  I remeasured the || combination of the caps - after
> unsoldering they were sometimes as much as half the value they should have
> been  - until they cooled right down and approached room temp. Occasionally
> a cap value approaching correct would show up on the meter once in a
> while - but that was was probably just coincidence :-)
> And yes, I did double, triple and quadruple check the meter against good
> caps - it was OK every time.
>
> These little blue things appear to have a huge temperature coefficent - are
> completely useless, designed to do nothing of value, and all have now gone
> into the waste bin.
> In fact, I was wondering if they were random-capacitors.
>
> I did have a just two trusted 22nF caps in the junk box that were within 20
> - 30% of the right values for the amp and an awful lot of 3.3nF 1700V things
> of a more respectable heritage, so just put these into the circuit, tested
> at 12V and got waveforms almost correct.   Increased drive freq to 515kHz
> (no real scope for changing cap values at this stage, so freq change would
> be easier to try with) where the waveform looked best, and increased supply
> volts.      Got to 30V and it was delivering 150 Watts; 40V and was getting
> around 350 Watts at which point I assumed it was going to work, so switched
> off for a break.   Wasn't going to tempt fate by gong to the full 50V having
> not even bothered to tune things up properly
> A picture of that breadboard can be seen at
> http://www.g4jnt.com/Download/ClassE_BrdBd01.jpg
>
> The yellow cap shunting the device was running quite warm - which is hardly
> surprising just a single poly[whatever] carrying all those amps - and the
> one in series with the tank was slightly warm.    So, now need to browse the
> Farnell catalogue (the cubic printed paper version is easier) for some caps
> that will do the job properly - like more of those yellow ones.  Actually,
> may have enough of the 3.3nF ones, but that would end up with lots in
> parallel
>
> So, for anyone who is contemplating a class E amplifier design:
>
> Get close to the calculated component values and it will probably
> mostly-work immediately.
> Play with the drive frequency while monitoring waveforms  to see which way
> tuning needs to go
> Don't use cheap high voltage ceramic capacitors
> Don't use cheap high voltage ceramic capacitors
>
> They would work well in a random number generator tho.....
>
> Andy
> www.g4jnt.com
>
>
>

<Prev in Thread] Current Thread [Next in Thread>