inverting dc-dc converter circuit
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From: MooseFET on 29 Jan 2010 09:53 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. You can get opto-MOSFET switches as SSRs http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=OR521-ND If you are careful to not have the source legs be the ones that move, you can use a capacitively coupled gate drive on a low Vth MOSFET and save on the current for driving the LEDs. If you use a sine wave to drive the MOSFETs, you can have their switching be very soft and hence low noise. An N channel and P channel MOSFET pair can switch one end of a capacitor from +15 to ground. An N channel and P channel MOSFET pair can switch one end of a capacitor from ground to -15 An N channel and P channel MOSFET pair can switch one end of a capacitor from -15 to ground. An N channel and P channel MOSFET pair can switch one end of a capacitor from -30 to -15 It looks like 8 MOSFETs plus two working capacitors would do it. > > John
From: Jim Thompson on 29 Jan 2010 09:57 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. Larkin and Obama are out of the same mold... mediocre talent, yet excessive ego ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: don on 29 Jan 2010 10:13 John Larkin wrote: >>>> John Larkin wrote: >>>> >>>>> homebrew single-inductor flyback converter, which circuit I've posted >>>>> here some time back. If you still have this circuit handy, please re-post. don
From: George Herold on 29 Jan 2010 10:26 On Jan 29, 12:27 am, 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 'bout a 48V power supply and define ground where you want it? Or do you need most of the 'poop' at +15 Volts? George H.
From: John Larkin on 29 Jan 2010 13:57
On Fri, 29 Jan 2010 17:54:01 +1100, Sylvia Else <sylvia(a)not.at.this.address> wrote: >John Larkin 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. > >Diode forward drops would be an issue if you really need -30 and are >trying to use a doubler circuit. Otherwise, for the benefit of the rest >of us, why wouldn't it work? > >Sylvia. The 555 would only swing about 13 volts p-p. Then you get to start in on diode drops. The 555 edges are ballpark 100 ns, noisy. 555s have supply shoot-through, ditto. John |