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Switching rail splitter

Hi, All,

I'm entirely sure this isn't a new technique, but it was new to me and fit my application very well--I needed +15 and -4 for analogue stuff and

+3.3 for a micro, all from a 24V brick. Current drain is maybe 100 mA each at most. The PA2004 is a nice trifilar toroid, with a 6 x 9 mm footprint. Wiring two sections in parallel reduced the series resistance in the low-voltage section. There are LDOs in both outputs.

I've also put it at

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Cheers

Phil Hobbs

Version 4 SHEET 1 992 680 WIRE -64 48 -80 48 WIRE 80 48 0 48 WIRE 144 48 80 48 WIRE -656 80 -720 80 WIRE -544 80 -576 80 WIRE -528 80 -544 80 WIRE -416 80 -448 80 WIRE -384 80 -416 80 WIRE -256 80 -304 80 WIRE -224 80 -256 80 WIRE -128 80 -160 80 WIRE -720 96 -720 80 WIRE -544 96 -544 80 WIRE -416 96 -416 80 WIRE -128 112 -128 80 WIRE -912 128 -1136 128 WIRE -864 128 -912 128 WIRE 144 128 144 48 WIRE 80 144 80 48 WIRE -256 160 -256 80 WIRE -992 176 -1024 176 WIRE -784 176 -912 176 WIRE -544 176 -544 160 WIRE -416 176 -416 160 WIRE -304 176 -352 176 WIRE -720 192 -720 176 WIRE 352 192 240 192 WIRE 448 192 416 192 WIRE -864 208 -864 128 WIRE -1136 224 -1136 128 WIRE -304 224 -320 224 WIRE -1024 240 -1024 176 WIRE -896 240 -1024 240 WIRE -784 240 -784 176 WIRE -784 240 -816 240 WIRE -608 240 -784 240 WIRE -320 240 -320 224 WIRE -320 240 -608 240 WIRE 80 240 80 208 WIRE 144 240 144 208 WIRE 144 240 80 240 WIRE -1024 256 -1024 240 WIRE -256 256 -256 240 WIRE -80 256 -80 48 WIRE -80 256 -256 256 WIRE 144 256 144 240 WIRE 240 256 240 192 WIRE 240 256 144 256 WIRE 352 256 240 256 WIRE 448 256 448 192 WIRE 448 256 416 256 WIRE 496 256 448 256 WIRE 576 256 496 256 WIRE -896 272 -912 272 WIRE -256 272 -256 256 WIRE 496 272 496 256 WIRE 576 272 576 256 WIRE -320 288 -320 240 WIRE -304 288 -320 288 WIRE 16 288 -64 288 WIRE 144 288 144 256 WIRE 144 288 16 288 WIRE -880 320 -880 304 WIRE -864 320 -864 304 WIRE -864 320 -880 320 WIRE 16 320 16 288 WIRE 144 320 144 288 WIRE -352 336 -352 176 WIRE -320 336 -352 336 WIRE -304 336 -320 336 WIRE -64 336 -64 288 WIRE -1136 352 -1136 304 WIRE -864 352 -864 320 WIRE -864 352 -1136 352 WIRE 496 352 496 336 WIRE -1136 368 -1136 352 WIRE 576 368 576 352 WIRE -912 384 -912 272 WIRE -864 384 -912 384 WIRE -608 384 -608 240 WIRE -608 384 -784 384 WIRE -256 416 -256 352 WIRE -912 432 -912 384 WIRE -320 432 -320 336 WIRE -320 432 -912 432 WIRE -64 432 -64 400 WIRE 16 432 16 400 WIRE 144 432 144 400 WIRE -1024 480 -1056 480 WIRE -912 480 -912 432 WIRE -912 480 -944 480 WIRE -896 480 -912 480 WIRE -784 480 -816 480 WIRE 240 480 240 256 WIRE 336 480 240 480 WIRE 448 480 400 480 WIRE 480 480 448 480 WIRE 560 480 480 480 WIRE 480 496 480 480 WIRE 560 496 560 480 WIRE -784 512 -784 480 WIRE 240 560 240 480 WIRE 336 560 240 560 WIRE 448 560 448 480 WIRE 448 560 400 560 WIRE 480 576 480 560 WIRE 560 592 560 576 FLAG 144 432 0 FLAG 496 352 0 FLAG 576 368 0 FLAG 576 256 Plus FLAG 480 576 0 FLAG 560 592 0 FLAG 560 480 Minus FLAG 16 432 0 FLAG -912 128 +5 FLAG -1056 480 +5 FLAG -784 512 0 FLAG -848 304 0 FLAG -1024 320 0 FLAG -1136 368 0 FLAG -720 192 0 FLAG -256 416 0 FLAG -128 112 0 FLAG -416 176 0 FLAG -544 176 0 FLAG -64 432 0 SYMBOL ind2 128 112 R0 SYMATTR InstName L1 SYMATTR Value 437u SYMATTR Type ind SYMATTR SpiceLine Rser=0.8 SYMBOL cap 480 272 R0 SYMATTR InstName C2 SYMATTR Value 1u SYMBOL res 560 256 R0 SYMATTR InstName R1 SYMATTR Value 60 SYMBOL cap 0 32 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 1u SYMBOL cap 464 496 R0 SYMATTR InstName C4 SYMATTR Value 1u SYMBOL res 544 480 R0 SYMATTR InstName R2 SYMATTR Value 50 SYMBOL Comparators\\LT1016 -864 192 R0 SYMATTR InstName U1 SYMBOL voltage -1136 208 R0 SYMATTR InstName V2 SYMATTR Value 5 SYMBOL res -800 464 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res -928 464 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 1200 SYMBOL res -768 368 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 1k SYMBOL cap -1040 256 R0 WINDOW 3 43 42 Left 2 SYMATTR Value 150p SYMATTR InstName C1 SYMBOL res -896 160 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 1.8k SYMBOL voltage -720 80 R0 SYMATTR InstName V1 SYMATTR Value 24 SYMBOL sw -256 144 R0 WINDOW 3 45 59 Left 2 SYMATTR Value IDXh SYMATTR InstName S1 SYMBOL sw -256 256 R0 WINDOW 0 53 61 Left 2 SYMATTR InstName S2 SYMATTR Value IDXL SYMBOL schottky 352 240 M90 WINDOW 0 18 1 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMATTR Value PMEG2005EB SYMATTR Description Diode SYMATTR Type diode SYMBOL cap -160 64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 1u SYMATTR SpiceLine Rser=10m Lser=1.0n SYMBOL cap -400 160 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C6 SYMATTR Value 1u SYMATTR SpiceLine Rser=10m Lser=1.5n SYMBOL ind -400 96 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L4 SYMATTR Value 10u SYMATTR SpiceLine Rser=0.2 SYMBOL cap -560 96 R0 SYMATTR InstName C7 SYMATTR Value 22u SYMATTR SpiceLine Rser=2 SYMBOL ind -544 96 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 60 107 VBottom 2 SYMATTR InstName L5 SYMATTR Value 40n SYMATTR SpiceLine Rser=50m SYMBOL res -560 64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 2 SYMBOL schottky 400 464 R90 WINDOW 0 13 78 VBottom 2 WINDOW 3 37 57 VTop 2 SYMATTR InstName D1 SYMATTR Value PMEG2005EB SYMATTR Description Diode SYMATTR Type diode SYMBOL ind2 128 304 R0 SYMATTR InstName L2 SYMATTR Value 437u SYMATTR Type ind SYMATTR SpiceLine Rser=0.8 SYMBOL ind2 0 304 R0 SYMATTR InstName L3 SYMATTR Value 437u SYMATTR Type ind SYMATTR SpiceLine Rser=0.8 SYMBOL cap 64 144 R0 SYMATTR InstName C8 SYMATTR Value 2p SYMBOL cap -80 336 R0 SYMATTR InstName C9 SYMATTR Value 4p SYMBOL schottky 352 176 M90 WINDOW 0 8 -6 VBottom 2 WINDOW 3 -16 148 VTop 2 SYMATTR InstName D2 SYMATTR Value PMEG2005EB SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 400 544 R90 WINDOW 0 9 69 VBottom 2 WINDOW 3 34 48 VTop 2 SYMATTR InstName D4 SYMATTR Value PMEG2005EB SYMATTR Description Diode SYMATTR Type diode TEXT -8 480 Left 2 !k1 L1 L2 L3 0.995 TEXT -184 624 Left 2 !.tran 0 1.5m 0 100n TEXT -560 504 Left 2 !.model IDXh sw(Ron=1.25 Roff=10meg Vt=0.25 vh=-.2) TEXT -8 264 Left 2 ;PA2004NL TEXT -456 464 Left 2 ;IDXN602 (two sections in parallel) TEXT -576 0 Left 2 ;decoupling TEXT -832 328 Left 2 ;Really a FIN1018 TEXT -872 568 Left 2 !.MODEL DI_B340A D ( IS=9.90n RS=14.0m BV=40.0 IBV=500u\n+ CJO=46.4p M=0.333 N=0.775 TT=7.20n ) TEXT -560 528 Left 2 !.model IDXL sw(Ron=1.25 Roff=10meg Vt=0.25 vh=-.2) TEXT 32 8 Left 3 ;Autotransformer Rail Splitter, +24 -> +4 & -5 TEXT 272 56 Left 2 ;Phil Hobbs\nElectroOptical Innovations LLC\nNovember

9, 2018 TEXT -1176 400 Left 2 ;Duty cycle sets ratio \nof +/- outputs TEXT 248 408 Left 2 ;Diodes are actually a single B340AF\nper side RECTANGLE Normal 208 416 -16 96 2 RECTANGLE Normal -144 384 -368 144 2 
--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs
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That's cute. But we are buying this

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for under $5, which is sure easy. A little extra EMI filtering would be prudent if noise matters.

I have some load test data on that one.

We use the 24 to +-15 version too, even when isolation isn't needed.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Hmm, I'd need more of a hint to find it on your web site.

But as JL says below I do like Cui DC-DC converters. (I'm partial to through hole) these seem much to cheap.

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And this looks like something I should buy..

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If you're winding a toroid there may be a lot less magnetic field 'crud'.

George H.

Reply to
George Herold

Opps forget that, Vmax = 13.2, some automotive thing. GH

Reply to
George Herold

Right, it's at

.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs

That one switches at 100 kHz, which is right in the middle of the band I care about. The one I posted runs at a bit over 2 MHz, which (in this case) covers a multitude of sins. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs

Yeah, that's fine. For safety purposes, it should have a current limiter on the input, or something like that (which would brown out the gate driver, activating UVLO, so it would go into a hiccup limiting mode, which isn't entirely a bad thing I guess). It's going fast enough that per-cycle protection doesn't really matter. It's also a charge pump (transformer coupled) which means you should watch for startup current and surge currents (which of course is what the supply filter is there for).

Can save a chip with a two-input gate driver, I think? Well, they're not comparator inputs (usually), so you'd be depending on the -in hysteresis, which isn't as reliable. *shrug*

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

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Reply to
Tim Williams

Sorry,

I'm using a cute little trifilar toroid,

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

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