inverting dc-dc converter circuit
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From: John Larkin on 30 Jan 2010 13:00 On Sat, 30 Jan 2010 15:55:58 +0100, Fred Bartoli <" "> wrote: >John Larkin a �crit : >> On Fri, 29 Jan 2010 19:35:29 -0800 (PST), MooseFET >> <kensmith(a)rahul.net> wrote: >> >>> On Jan 28, 9:27 pm, John Larkin >>> <jjSNIPlar...(a)highTHISlandtechnology.com> wrote: >>>> This afternoon we were talking with Phil Hobbs about an >>>> electro-optical thingie we're doing. The prime power is a +15 volt >>>> wall wart, and we need -30 internally to power some photodiodes and >>>> opamps and stuff, 30 mA maybe. Our design currently has a cute >>>> homebrew single-inductor flyback converter, which circuit I've posted >>>> here some time back. We are concerned about having such a potentially >>>> noisy gadget on the same small board with nanoamp signals. >>>> >>>> I proposed a different circuit: imagine eight opto-SSRs and two >>>> capacitors. A low frequency clock, 400 Hz maybe, switches 4 of them on >>>> and 4 off, alternately. The arrangement connects the two caps in >>>> parallel to the +15 supply, charging them up. Then it disconnects them >>>> and then restacks them in series such as to make -30 to ground. The >>>> low frequency and fairly soft switching edges should make this pretty >>>> quiet. >>>> >>>> Phil named this the Groucho Marx Generator. >>>> >>>> John >>> How about a couple of LTC1144s? >> >> They are only good for 18 volts, and their switch resistance is high, >> 120 ohms, so my 30 mA load would whack them. The Groucho circuit is >> just a homebrew equivalent. >> >> John >> > >The real Groucho Marx generator uses relays. The big ones, multi megavolts, charge a row of caps in parallel using liquid resistors, and stack them in series using laser-triggered spark gaps. John
From: John Larkin on 30 Jan 2010 13:05 On Sat, 30 Jan 2010 09:58:57 -0600, mook Johnson <mook(a)mook.net> wrote: >On 1/28/2010 11:27 PM, John Larkin wrote: >> >> >> This afternoon we were talking with Phil Hobbs about an >> electro-optical thingie we're doing. The prime power is a +15 volt >> wall wart, and we need -30 internally to power some photodiodes and >> opamps and stuff, 30 mA maybe. Our design currently has a cute >> homebrew single-inductor flyback converter, which circuit I've posted >> here some time back. We are concerned about having such a potentially >> noisy gadget on the same small board with nanoamp signals. >> >> I proposed a different circuit: imagine eight opto-SSRs and two >> capacitors. A low frequency clock, 400 Hz maybe, switches 4 of them on >> and 4 off, alternately. The arrangement connects the two caps in >> parallel to the +15 supply, charging them up. Then it disconnects them >> and then restacks them in series such as to make -30 to ground. The >> low frequency and fairly soft switching edges should make this pretty >> quiet. >> >> Phil named this the Groucho Marx Generator. >> >> >> John >> > >What kind of regulation do you need on the -30V? Is that 30mA constant >or does it move around a lot between 0 and 30mA? > Load is pretty constant and stability of maybe a half a volt would be OK. The +15 is well regulated, so a non-regulated charge pump would work if it was fairly stiff. In real life, we'll probably use the inverting flyback with a very well-managed layout and an option for a deep-drawn aluminum cover in case it's needed. I still want to do something with the Groucho circuit. It can also be a floating supply, up to the SSR voltage limits. John
From: Joerg on 30 Jan 2010 14:19 John Larkin wrote: > On Sat, 30 Jan 2010 09:58:57 -0600, mook Johnson <mook(a)mook.net> > wrote: > >> On 1/28/2010 11:27 PM, John Larkin wrote: >>> >>> This afternoon we were talking with Phil Hobbs about an >>> electro-optical thingie we're doing. The prime power is a +15 volt >>> wall wart, and we need -30 internally to power some photodiodes and >>> opamps and stuff, 30 mA maybe. Our design currently has a cute >>> homebrew single-inductor flyback converter, which circuit I've posted >>> here some time back. We are concerned about having such a potentially >>> noisy gadget on the same small board with nanoamp signals. >>> >>> I proposed a different circuit: imagine eight opto-SSRs and two >>> capacitors. A low frequency clock, 400 Hz maybe, switches 4 of them on >>> and 4 off, alternately. The arrangement connects the two caps in >>> parallel to the +15 supply, charging them up. Then it disconnects them >>> and then restacks them in series such as to make -30 to ground. The >>> low frequency and fairly soft switching edges should make this pretty >>> quiet. >>> >>> Phil named this the Groucho Marx Generator. >>> >>> >>> John >>> >> What kind of regulation do you need on the -30V? Is that 30mA constant >> or does it move around a lot between 0 and 30mA? >> > > Load is pretty constant and stability of maybe a half a volt would be > OK. The +15 is well regulated, so a non-regulated charge pump would > work if it was fairly stiff. > > In real life, we'll probably use the inverting flyback with a very > well-managed layout and an option for a deep-drawn aluminum cover in > case it's needed. > Put an LC behind it and you should be fine. If you pay attention to component height you can get away with standard shield covers, no fancy aluminum needed. [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: whit3rd on 30 Jan 2010 14:42 On Jan 30, 10:05 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> This afternoon we were talking with Phil Hobbs about an > >> electro-optical thingie we're doing. The prime power is a +15 volt > >> wall wart, and we need -30 internally to power some photodiodes and > >> opamps and stuff, 30 mA maybe. > In real life, we'll probably use the inverting flyback with a very > well-managed layout and an option for a deep-drawn aluminum cover in > case it's needed. You're making life hard for yourself. Switch the wallwart for a 20 VAC version, and all the problems go away (including calibration sensitvity on the external regulated voltage). Linear or switching regulation of your 15V should be a simple matter, and -30V bias is also easy.
From: miso on 30 Jan 2010 16:28
On Jan 29, 2:35 pm, Bill Sloman <bill.slo...(a)ieee.org> wrote: > On Jan 29, 3:57 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- > > Web-Site.com> wrote: > > On Thu, 28 Jan 2010 22:32:10 -0800, Muzaffer Kal <k...(a)dspia.com> > > wrote: > > > >On Thu, 28 Jan 2010 22:05:37 -0800, John Larkin > > ><jjSNIPlar...(a)highTHISlandtechnology.com> wrote: > > > >>On Thu, 28 Jan 2010 23:56:41 -0600, Vladimir Vassilevsky > > >><nos...(a)nowhere.com> wrote: > > > >>>John Larkin wrote: > > <snip> > > > >>It's incredible that you think it might. Stick to digital. > > > >>John > > > >You mean this doesn't work:http://www.csgnetwork.com/ne555c1.html? > > >Give it a try. > > > Larkin and Obama are out of the same mold... mediocre talent, yet > > excessive ego ;-) > > Whereas Jim's egomania is justified by his stellar reputation amongst > integrated circuit designers? Bob Widlar, Barry Gilbert and Hans > Camenzind recognised him as comparable talent? Had every actually > heard of him? > > -- > Bill Sloman, Nijmegen To some extent, Widlar and Gilbert were around when there was basic circuitry to discover. Not quite so for Camenzind who was more of an out of the box thinker. So maybe Widlar and Gilbert were there at the right time. Also Wilson, whom I met years ago. All great thinkers, but also there at a time when their intellect could be applied. However, I see your point. My opinion is people who constantly self promote really aren't even 10% as good as they say they are. It's right up there with the people who spend a lot of time telling you how hard they work. |