inverting dc-dc converter circuit
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From: Sylvia Else on 29 Jan 2010 02:44 Muzaffer Kal wrote: > On Thu, 28 Jan 2010 22:05:37 -0800, John Larkin > <jjSNIPlarkin(a)highTHISlandtechnology.com> wrote: > >> On Thu, 28 Jan 2010 23:56:41 -0600, Vladimir Vassilevsky >> <nospam(a)nowhere.com> wrote: >> >>> >>> 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. >>> Incredible. >>> >>> Why a 555 with a trivial diode-capacitor voltage multiplier won't work? >>> >>> >>> VLV >> >> 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. Well, it wouldn't even produce -15v from +15v, let alone -30v. Sylvia.
From: legg on 29 Jan 2010 06:39 On Thu, 28 Jan 2010 21:27:10 -0800, John Larkin <jjSNIPlarkin(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 > At least one more cap to keep droop below 10% ppk. 25uF The switched caps would have to be 5 or 10x multiples of this to maintain anywhere near 30V after the transfer. With half the energy transfer lost in switching, thats 120mA drawn from the 15V rail. Not small anymore. There are quieter conversion methods than flyback or switched caps. Harpo was mute. RL
From: Robert Elson on 29 Jan 2010 09:16 What make SSRs "fairly soft switching edges"? May be better to make a sin generator and a transformer?
From: John Larkin on 29 Jan 2010 09:46 On Fri, 29 Jan 2010 06:16:39 -0800 (PST), Robert Elson <elsonrobert(a)gmail.com> wrote: >What make SSRs "fairly soft switching edges"? >May be better to make a sin generator and a transformer? The PV-powered gate drivers are very weak, so the switching edges are slow, far slower than a 555's. And the fets go from resistive to constant-current at higher voltage drops, which further softens things up. And SSRs are fast-break, slow-make, so there's no shoot-through. John
From: John Larkin on 29 Jan 2010 09:49
On Thu, 28 Jan 2010 22:32:10 -0800, Muzaffer Kal <kal(a)dspia.com> wrote: >On Thu, 28 Jan 2010 22:05:37 -0800, John Larkin ><jjSNIPlarkin(a)highTHISlandtechnology.com> wrote: > >>On Thu, 28 Jan 2010 23:56:41 -0600, Vladimir Vassilevsky >><nospam(a)nowhere.com> wrote: >> >>> >>> >>>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. >>> >>>Incredible. >>> >>>Why a 555 with a trivial diode-capacitor voltage multiplier won't work? >>> >>> >>>VLV >> >> >>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. There's no point to trying it. It's obvious that it wouldn't meet my requirements. Stick to digital. John |