On 06/24/2013 11:59 AM, JW wrote:
All the ground transients are contained inside the cups. Ripple on the supply and ground traces is in the low nanoamps.
I used to try pretty hard to avoid SMPSes, but at this point they're pretty much a necessary evil. Toroids are a big help.
I can't find the exact circuit at the moment, but it was something like this with an extra cap multiplier stage. IIRC I decided to leave the second stage out, since the ripple current was in the low nanoamps anyway. The heater was a bunch of 0603 resistors on a flex, indium-soldered to a thermal shield made of anodized, annealed aluminum foil for fast response.
Not the most efficient thing in the world, but interesting in some respects. The FB loop may need a bit of recompensating--I gave up after about 15 ms of simulated time.
Cheers
Phil Hobbs
Version 4 SHEET 1 1892 2928 WIRE 64 -160 -304 -160 WIRE 176 -160 144 -160 WIRE 240 -160 176 -160 WIRE 496 -160 240 -160 WIRE -304 -128 -304 -160 WIRE 496 -128 496 -160 WIRE 176 -64 176 -96 WIRE 240 -64 240 -160 WIRE 576 -32 560 -32 WIRE 688 -32 656 -32 WIRE -304 -16 -304 -48 WIRE 496 -16 496 -48 WIRE 496 -16 432 -16 WIRE 560 32 560 -32 WIRE 576 32 560 32 WIRE 688 32 688 -32 WIRE 688 32 656 32 WIRE 736 32 688 32 WIRE 736 48 736 32 WIRE 64 80 -80 80 WIRE 240 80 240 16 WIRE 240 80 64 80 WIRE -80 112 -80 80 WIRE 64 128 64 80 WIRE 64 144 64 128 WIRE 304 144 240 144 WIRE 368 144 304 144 WIRE 496 144 496 80 WIRE 496 144 368 144 WIRE 240 160 240 144 WIRE 736 160 736 112 WIRE 496 176 496 144 WIRE 560 176 496 176 WIRE 656 176 656 32 WIRE 656 176 640 176 WIRE -80 208 -80 176 WIRE 304 208 304 144 WIRE 496 208 496 176 WIRE 496 288 496 272 WIRE 368 304 368 144 WIRE 432 304 432 -16 WIRE 64 352 64 192 WIRE 240 352 240 304 WIRE 240 352 64 352 WIRE 304 352 304 288 WIRE 304 352 240 352 WIRE 304 368 304 352 WIRE -512 384 -544 384 WIRE -416 384 -432 384 WIRE -352 384 -416 384 WIRE -208 384 -352 384 WIRE -208 400 -208 384 WIRE 432 400 432 384 WIRE 496 400 432 400 WIRE 592 400 560 400 WIRE -240 416 -304 416 WIRE 16 416 -128 416 WIRE 112 416 16 416 WIRE 432 416 432 400 WIRE -544 432 -544 384 WIRE -128 432 -128 416 WIRE -128 432 -176 432 WIRE 592 432 592 400 WIRE -240 448 -272 448 WIRE 112 448 112 416 WIRE 128 448 112 448 WIRE 256 448 208 448 WIRE -352 480 -352 464 WIRE -304 480 -304 416 WIRE -304 480 -352 480 WIRE -352 496 -352 480 WIRE -352 496 -416 496 WIRE -208 496 -208 464 WIRE 304 496 304 464 WIRE -416 512 -416 496 WIRE -352 512 -352 496 WIRE -272 528 -272 448 WIRE 368 528 368 368 WIRE 368 528 -272 528 WIRE 432 528 432 496 WIRE 432 528 368 528 WIRE -544 544 -544 512 WIRE 432 544 432 528 WIRE -416 608 -416 576 WIRE -352 608 -352 592 WIRE -352 608 -416 608 WIRE 16 608 16 416 WIRE -352 624 -352 608 WIRE 432 656 432 624 WIRE 16 752 16 672 FLAG -304 -16 0 FLAG -304 -160 +48 FLAG 304 496 0 FLAG 496 288 0 FLAG 432 656 0 FLAG -544 544 0 FLAG -208 496 0 FLAG -352 624 0 FLAG 736 160 0 FLAG 16 752 0 FLAG -80 208 0 FLAG -416 496 set FLAG 432 -16 out FLAG 176 -64 0 FLAG 592 432 0 FLAG -416 448 0 SYMBOL voltage -304 -144 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 144 Left 2 WINDOW 3 24 44 Left 2 SYMATTR Value 48 SYMATTR InstName V1 SYMBOL Misc\\2N7002 256 368 R0 SYMATTR InstName U1 SYMBOL ind 288 192 R0 SYMATTR InstName L1 SYMATTR Value 68u SYMATTR SpiceLine Ipk=320m Rser=1.3 Rpar=100k Cpar=2p SYMBOL cap 480 208 R0 SYMATTR InstName C1 SYMATTR Value 330n SYMBOL res 480 -144 R0 SYMATTR InstName R1 SYMATTR Value 500 SYMBOL res 224 432 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 200 SYMBOL res 416 400 R0 SYMATTR InstName R3 SYMATTR Value 500k SYMBOL res 416 528 R0 SYMATTR InstName R4 SYMATTR Value 80k SYMBOL voltage -544 416 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 144 Left 2 SYMATTR InstName V2 SYMATTR Value 5v SYMBOL res -368 368 R0 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res -368 496 R0 SYMATTR InstName R6 SYMATTR Value {vset/(5-vset)*1k} SYMBOL pnp 560 80 R180 SYMATTR InstName Q1 SYMATTR Value BC857B SYMBOL polcap 720 48 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 4.7u SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=63 Irms=170m Rser=0.05 Lser=0 SYMBOL res 224 208 R0 WINDOW 0 -49 55 Left 2 WINDOW 3 -118 111 Left 2 SYMATTR InstName R8 SYMATTR Value {Rsnub} SYMBOL cap 224 160 R0 WINDOW 0 -42 8 Left 2 WINDOW 3 -54 -38 Left 2 SYMATTR InstName C3 SYMATTR Value {Csnub} SYMBOL schottky 32 672 R180 WINDOW 0 24 72 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D2 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL Comparators\\LT1720 -208 368 R0 SYMATTR InstName U2 SYMBOL diode 80 192 R180 WINDOW 0 24 72 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value BAV70 SYMBOL cap 352 304 R0 SYMATTR InstName C4 SYMATTR Value 10n SYMBOL cap -432 512 R0 SYMATTR InstName C5 SYMATTR Value 1 SYMBOL cap -64 176 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C6 SYMATTR Value 4.7u SYMBOL res 224 -80 R0 SYMATTR InstName R9 SYMATTR Value 250 SYMBOL res 560 48 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R10 SYMATTR Value 25 SYMBOL res 656 160 R90 WINDOW 0 -16 76 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 2k SYMBOL cap 192 -96 R180 WINDOW 0 31 2 Left 2 WINDOW 3 75 -34 Left 2 SYMATTR InstName C7 SYMATTR Value 4.7u SYMBOL res 160 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 -39 -4 VTop 2 SYMATTR InstName R12 SYMATTR Value 2 SYMBOL ind 560 -16 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L2 SYMATTR Value 100n SYMBOL res 416 288 R0 SYMATTR InstName R7 SYMATTR Value 500k SYMBOL cap 560 384 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C8 SYMATTR Value 1n SYMBOL res -528 400 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R13 SYMATTR Value 10 SYMBOL cap -432 384 R0 SYMATTR InstName C9 SYMATTR Value 4.7u TEXT -224 896 Left 2 !.tran 0 100m 0 50n TEXT 504 728 Left 2 !.param vset=1.5 TEXT 496 792 Left 2 !;.step param vset list 1m.1 0.2 0.4 0.8 1.5 2.5 3.2
3.4 3.5 3.6 3.8 TEXT 504 848 Left 2 !;.step param Rsnub 1100 1600 100 TEXT 504 680 Left 2 !.param Rsnub=6000 TEXT 864 680 Left 2 !.param Csnub=22p TEXT 496 760 Left 2 !;.step param Csnub list 180p 200p 220p 270p 330p 390p 470p TEXT -800 664 Left 2 !.MODEL BAV70 D \n + IS = 3.2E-009 \n + N = 1.85 \n + BV = 125.9 \n + IBV = 2.906E-007 \n + RS = 1.1 \n- CJO = 4.957E-013 \n + VJ = 0.54 \n + M = 0.03 \n + FC =