inverting dc-dc converter circuit
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From: John Larkin on 31 Jan 2010 16:47 On Sat, 30 Jan 2010 11:42:01 -0800 (PST), whit3rd <whit3rd(a)gmail.com> wrote: >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. We have the 15 volt Phihong switching-regulated wart in stock, and its international plug adapter kit, and we can send them anywhere in the world. John
From: John Larkin on 31 Jan 2010 17:09 On 31 Jan 2010 15:29:31 GMT, Glen Walpert <nospam(a)null.void> wrote: >On Sat, 30 Jan 2010 10:05:13 -0800, 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. >> >> I still want to do something with the Groucho circuit. It can also be a >> floating supply, up to the SSR voltage limits. >> >> John > >Have you read Linear AN's 70 and 85, where Jim Williams presents a bunch >of example designs for low current bias supplies with less than 100 uV >noise? The flyback was the worst of the topologies discussed from a >noise perspective. An85 is a simple boost, same as a flyback. Even a Cuk has fast currents being switched into different ground nodes. The trick with any switcher is to manage the layout so that ground-injected currents don't find their way into sensitive stuff on the same board. Slowing down the gate drive (tweaking the gate resistor) can reduce spikes at the cost of some efficiency. Frequency modulation (spread spectrum) is helpful here too; we'll include hooks for that, just in case.[1] ftp://jjlarkin.lmi.net/SS_LTC3411.zip Here's the switching waveform from an LM3102 synchronous switcher, ftp://jjlarkin.lmi.net/SwitcherRise.JPG which clearly shows the substrate diode of the lower output fet acting like a step-recovery diode. This trashed opamps four inches away. John [1] Phil pointed out that high-C varicaps are rare these days. I wonder if any common power diodes would make decent, maybe 100 or 200 pF, varicaps. Schottky, maybe.
From: Joerg on 31 Jan 2010 17:16 John Larkin wrote: > On 31 Jan 2010 15:29:31 GMT, Glen Walpert <nospam(a)null.void> wrote: > >> On Sat, 30 Jan 2010 10:05:13 -0800, 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. >>> >>> I still want to do something with the Groucho circuit. It can also be a >>> floating supply, up to the SSR voltage limits. >>> >>> John >> Have you read Linear AN's 70 and 85, where Jim Williams presents a bunch >> of example designs for low current bias supplies with less than 100 uV >> noise? The flyback was the worst of the topologies discussed from a >> noise perspective. > > An85 is a simple boost, same as a flyback. Even a Cuk has fast > currents being switched into different ground nodes. The trick with > any switcher is to manage the layout so that ground-injected currents > don't find their way into sensitive stuff on the same board. > > Slowing down the gate drive (tweaking the gate resistor) can reduce > spikes at the cost of some efficiency. Frequency modulation (spread > spectrum) is helpful here too; we'll include hooks for that, just in > case.[1] > > ftp://jjlarkin.lmi.net/SS_LTC3411.zip > > Here's the switching waveform from an LM3102 synchronous switcher, > > ftp://jjlarkin.lmi.net/SwitcherRise.JPG > > which clearly shows the substrate diode of the lower output fet acting > like a step-recovery diode. This trashed opamps four inches away. > Probably could be "snubbered" but of course that costs efficiency, too. > John > > [1] Phil pointed out that high-C varicaps are rare these days. I > wonder if any common power diodes would make decent, maybe 100 or 200 > pF, varicaps. Schottky, maybe. > Because nobody makes decent AM radios anymore :-( But these are still large qty stock, 68pF: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ZMV835ATR-ND FETs as variable resistors are nice though, if needed they can be servoed in a dual-package. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jamie on 31 Jan 2010 18:03 MooseFET wrote: > On Jan 31, 7:29 am, Glen Walpert <nos...(a)null.void> wrote: > >>On Sat, 30 Jan 2010 10:05:13 -0800, John Larkin wrote: >> >>>On Sat, 30 Jan 2010 09:58:57 -0600, mook Johnson <m...(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 >> >>Have you read Linear AN's 70 and 85, where Jim Williams presents a bunch >>of example designs for low current bias supplies with less than 100 uV >>noise? The flyback was the worst of the topologies discussed from a >>noise perspective. > > > The Cuk converter is the best for inverted supplies. Still, the > capacitance > of the inductors lets some of the fast edges get through to the output > capacitor. The layout of the windings can help by putting the moving > end of > the output side near the nonmoving end of the input side. > in a pinch, I would use something like this for a low level -33 volts . I changed the values to fit the thread that was going on here. PS. It uses a 555 :), just to stir the pot! Version 4 SHEET 1 880 680 WIRE 240 -80 64 -80 WIRE 240 -64 240 -80 WIRE -192 -48 -320 -48 WIRE 64 -48 64 -80 WIRE 64 -48 -192 -48 WIRE 96 -16 80 -16 WIRE -192 48 -192 -48 WIRE -192 64 -192 48 WIRE -160 128 -192 128 WIRE 80 128 80 -16 WIRE 80 128 64 128 WIRE 240 128 240 32 WIRE 272 128 240 128 WIRE 400 128 336 128 WIRE 496 128 400 128 WIRE 240 144 240 128 WIRE 496 160 496 128 WIRE 400 176 400 128 WIRE -192 192 -192 128 WIRE -160 192 -192 192 WIRE 144 192 64 192 WIRE -320 256 -320 -48 WIRE -288 256 -320 256 WIRE -160 256 -288 256 WIRE 96 256 64 256 WIRE 240 256 240 224 WIRE 240 256 96 256 WIRE 400 256 400 240 WIRE 400 256 240 256 WIRE 496 256 496 224 WIRE 496 256 400 256 WIRE 96 288 96 256 WIRE -288 304 -288 256 WIRE -192 320 -192 272 WIRE 144 320 144 192 WIRE 144 320 -192 320 WIRE -192 336 -192 320 WIRE -288 400 -288 384 FLAG 96 288 0 FLAG -288 400 0 FLAG -192 400 0 SYMBOL Misc\\NE555 -48 160 R180 SYMATTR InstName U1 SYMBOL voltage -288 288 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMATTR SpiceLine Rser=0 SYMBOL res -208 32 R0 WINDOW 3 -64 71 Left 0 SYMATTR InstName R2 SYMATTR Value 2000 SYMBOL cap -208 336 R0 SYMATTR InstName C2 SYMATTR Value 0.01�f SYMBOL res -208 176 R0 WINDOW 3 -60 41 Left 0 SYMATTR InstName R1 SYMATTR Value 1500 SYMBOL ind 224 128 R0 SYMATTR InstName L1 SYMATTR Value 1mh SYMBOL schottky 336 112 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D2 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 384 176 R0 SYMATTR InstName C1 SYMATTR Value .5�f SYMBOL res 192 -32 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL pnp 176 32 M180 SYMATTR InstName Q1 SYMATTR Value BCW68F SYMBOL zener 480 160 R0 SYMATTR InstName D1 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode TEXT 416 408 Left 0 !.tran 0 0.010 0 1 startup
From: MooseFET on 31 Jan 2010 19:30
On Jan 31, 3:03 pm, Jamie <jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote: > MooseFET wrote: > > On Jan 31, 7:29 am, Glen Walpert <nos...(a)null.void> wrote: > > >>On Sat, 30 Jan 2010 10:05:13 -0800, John Larkin wrote: > > >>>On Sat, 30 Jan 2010 09:58:57 -0600, mook Johnson <m...(a)mook.net> wrote: > If you want more efficient operation, you could do this: Version 4 SHEET 1 880 680 WIRE 240 -80 64 -80 WIRE 240 -64 240 -80 WIRE -320 -48 -448 -48 WIRE 64 -48 64 -80 WIRE 64 -48 -320 -48 WIRE 96 -16 80 -16 WIRE -320 48 -320 -48 WIRE -320 64 -320 48 WIRE -160 128 -320 128 WIRE 80 128 80 -16 WIRE 80 128 64 128 WIRE 240 128 240 32 WIRE 272 128 240 128 WIRE 400 128 336 128 WIRE 720 128 400 128 WIRE 240 144 240 128 WIRE 720 160 720 128 WIRE 400 176 400 128 WIRE -320 192 -320 128 WIRE -160 192 -320 192 WIRE 144 192 64 192 WIRE -448 256 -448 -48 WIRE -416 256 -448 256 WIRE -160 256 -416 256 WIRE 96 256 64 256 WIRE 240 256 240 224 WIRE 240 256 96 256 WIRE 400 256 400 240 WIRE 400 256 240 256 WIRE 512 256 400 256 WIRE 720 256 720 224 WIRE 720 256 592 256 WIRE 96 288 96 256 WIRE -416 304 -416 256 WIRE 848 304 784 304 WIRE -320 320 -320 272 WIRE -192 320 -320 320 WIRE 144 320 144 192 WIRE 144 320 -192 320 WIRE -320 336 -320 320 WIRE -192 336 -192 320 WIRE 720 352 400 352 WIRE 144 368 144 320 WIRE 400 368 400 352 WIRE 400 368 144 368 WIRE -416 400 -416 384 WIRE -192 400 -320 400 FLAG 96 288 0 FLAG -416 400 0 FLAG -320 400 0 FLAG 848 304 0 SYMBOL Misc\\NE555 -48 160 R180 SYMATTR InstName U1 SYMBOL voltage -416 288 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR SpiceLine Rser=0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL res -336 32 R0 WINDOW 3 -64 71 Left 0 SYMATTR Value 2000 SYMATTR InstName R2 SYMBOL cap -208 336 R0 SYMATTR InstName C2 SYMATTR Value 0.01�f SYMBOL res -336 176 R0 WINDOW 3 -60 41 Left 0 SYMATTR Value 1500 SYMATTR InstName R1 SYMBOL ind 224 128 R0 SYMATTR InstName L1 SYMATTR Value 1mh SYMBOL schottky 336 112 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName D2 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 384 176 R0 SYMATTR InstName C1 SYMATTR Value .5�f SYMBOL res 192 -32 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 1k SYMBOL pnp 176 32 M180 SYMATTR InstName Q1 SYMATTR Value BCW68F SYMBOL zener 704 160 R0 SYMATTR InstName D1 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode SYMBOL npn 784 352 R180 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 608 240 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R4 SYMATTR Value 10k TEXT 416 408 Left 0 !.tran 0 0.010 0 1 startup |