I need a DC to DC boost circuit with an output defined not with respect to ground, but with respect to the input, which is variable. Output about 15 volts above the input, over a wide range -- from less than a volt in, up to
15 or 16 volts in. But can be inefficient and only needs to put out a few milliamps. I pasted an LTspice netlist of a possible solution. R15 simulates a grain-of-wheat incandescent. For Q6, if the Zetex is hard to find I might use a DSS416 or some such. What's the consensus about the vulnerability of Q6 when Vin = 16 volts?Version 4 SHEET 1 1388 680 WIRE 496 -160 -80 -160 WIRE 384 -144 352 -144 WIRE -80 -128 -80 -160 WIRE 352 -112 352 -144 WIRE 512 -112 352 -112 WIRE 560 -112 512 -112 WIRE 352 -80 352 -112 WIRE 448 -80 448 -144 WIRE 448 -80 416 -80 WIRE 512 -64 512 -112 WIRE -528 -16 -528 -48 WIRE -528 -16 -560 -16 WIRE -464 -16 -528 -16 WIRE -368 -16 -464 -16 WIRE -352 -16 -368 -16 WIRE -304 -16 -352 -16 WIRE -288 -16 -304 -16 WIRE -192 -16 -288 -16 WIRE -160 -16 -192 -16 WIRE 208 -16 -160 -16 WIRE 272 -16 208 -16 WIRE 288 -16 288 -112 WIRE 288 -16 272 -16 WIRE 304 -16 288 -16 WIRE 448 -16 448 -80 WIRE 448 -16 384 -16 WIRE -464 0 -464 -16 WIRE -192 0 -192 -16 WIRE 272 32 272 -16 WIRE 384 32 272 32 WIRE -368 48 -400 48 WIRE -256 48 -288 48 WIRE 272 48 272 32 WIRE 496 80 496 -160 WIRE 496 80 448 80 WIRE -464 96 -592 96 WIRE -448 96 -464 96 WIRE -384 96 -288 48 WIRE -352 96 -352 -16 WIRE -272 96 -368 48 WIRE -192 96 -208 96 WIRE -128 96 -192 96 WIRE 144 96 -128 96 WIRE 208 96 208 -16 WIRE -464 112 -464 96 WIRE -192 112 -192 96 WIRE -528 128 -528 -16 WIRE -304 128 -304 -16 WIRE -80 144 -80 -48 WIRE 16 144 -16 144 WIRE 272 144 272 128 WIRE 272 144 96 144 WIRE 352 144 352 -80 WIRE 352 144 336 144 WIRE 272 160 272 144 WIRE -464 208 -464 192 WIRE -416 208 -464 208 WIRE -352 208 -352 176 WIRE -192 208 -192 192 WIRE -192 208 -240 208 WIRE -160 208 -160 64 WIRE -160 208 -192 208 WIRE 208 208 208 176 WIRE 208 208 112 208 WIRE 208 224 208 208 WIRE -560 240 -560 64 WIRE -464 240 -464 208 WIRE -464 240 -560 240 WIRE -352 256 -304 208 WIRE -352 256 -400 256 WIRE -304 256 -352 208 WIRE -256 256 -304 256 WIRE -80 256 -80 144 WIRE -16 256 -80 256 WIRE 48 256 -16 256 WIRE 144 272 144 176 WIRE -592 320 -592 176 WIRE -528 320 -528 208 WIRE -528 320 -592 320 WIRE -464 320 -464 304 WIRE -464 320 -528 320 WIRE -384 320 -384 176 WIRE -384 320 -464 320 WIRE -352 320 -384 320 WIRE -304 320 -352 320 WIRE -272 320 -272 176 WIRE -272 320 -304 320 WIRE -192 320 -192 304 WIRE -192 320 -272 320 WIRE -128 320 -128 176 WIRE -128 320 -192 320 WIRE -80 320 -128 320 WIRE -16 320 -80 320 WIRE 112 320 112 304 WIRE 112 320 -16 320 WIRE 208 320 112 320 WIRE 272 320 272 256 WIRE 272 320 208 320 FLAG 560 -32 0 FLAG -528 -48 Vin FLAG 512 -64 Vout FLAG -80 320 0 SYMBOL npn -256 208 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL npn -400 208 M0 SYMATTR InstName Q2 SYMATTR Value 2N2222 SYMBOL pnp -400 96 R180 WINDOW 0 51 37 Left 2 WINDOW 3 31 60 Left 2 SYMATTR InstName Q3 SYMATTR Value 2N2907 SYMBOL pnp -256 96 M180 WINDOW 0 36 42 Left 2 WINDOW 3 -10 95 Left 2 SYMATTR InstName Q4 SYMATTR Value 2N2907 SYMBOL cap -240 192 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 1n SYMBOL cap -352 192 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 1n SYMBOL cap -384 80 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 1n SYMBOL cap -208 80 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 8 14 VTop 2 SYMATTR InstName C4 SYMATTR Value 1n SYMBOL res -320 112 R0 WINDOW 0 1 -2 Left 2 WINDOW 3 -13 62 Left 2 SYMATTR InstName R1 SYMATTR Value 47k SYMBOL res -400 80 R0 WINDOW 0 0 40 Left 2 WINDOW 3 -5 70 Left 2 SYMATTR InstName R3 SYMATTR Value 47k SYMBOL res -288 80 R0 WINDOW 0 1 42 Left 2 WINDOW 3 -2 72 Left 2 SYMATTR InstName R4 SYMATTR Value 4k7 SYMBOL voltage -528 112 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 -42 -248 Left 2 WINDOW 0 -13 58 Left 2 SYMATTR Value PULSE(0 1 0 100n) SYMATTR InstName V1 SYMBOL res -480 96 R0 WINDOW 0 3 55 Left 2 WINDOW 3 13 80 Left 2 SYMATTR InstName R5 SYMATTR Value 10 SYMBOL res -208 96 R0 WINDOW 0 -16 36 Left 2 WINDOW 3 -2 70 Left 2 SYMATTR InstName R6 SYMATTR Value 10 SYMBOL diode -288 320 R180 WINDOW 0 3 -13 Left 2 WINDOW 3 -84 -14 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode -336 320 R180 WINDOW 0 88 -13 Left 2 WINDOW 3 -1 -12 Left 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL diode -272 48 R180 WINDOW 0 8 108 Left 2 WINDOW 3 -29 82 Left 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode -352 48 R180 WINDOW 0 31 45 Left 2 WINDOW 3 9 94 Left 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL res -368 80 R0 WINDOW 0 6 32 Left 2 WINDOW 3 9 71 Left 2 SYMATTR InstName R2 SYMATTR Value 4k7 SYMBOL res -608 80 R0 WINDOW 0 17 38 Left 2 WINDOW 3 2 88 Left 2 SYMATTR InstName R7 SYMATTR Value 4k7 SYMBOL res -576 -32 R0 WINDOW 0 -3 53 Left 2 WINDOW 3 -12 89 Left 2 SYMATTR InstName R8 SYMATTR Value 4k7 SYMBOL res -144 80 R0 WINDOW 0 15 38 Left 2 WINDOW 3 7 73 Left 2 SYMATTR InstName R9 SYMATTR Value 4k7 SYMBOL res -176 -32 R0 SYMATTR InstName R10 SYMATTR Value 4k7 SYMBOL npn 144 224 R0 SYMATTR InstName Q5 SYMATTR Value 2N2222 SYMBOL npn 208 160 R0 WINDOW 0 56 45 Left 2 SYMATTR InstName Q6 SYMATTR Value FZT849 SYMBOL ind 256 32 R0 WINDOW 3 64 53 Left 2 SYMATTR Value 100µ SYMATTR InstName L1 SYMATTR SpiceLine Rser=.5 SYMBOL schottky 272 160 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D5 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL pnp 384 80 M180 SYMATTR InstName Q8 SYMATTR Value 2N2907 SYMBOL zener 416 -96 R90 WINDOW 0 -4 32 VBottom 2 WINDOW 3 37 -14 VTop 2 SYMATTR InstName D6 SYMATTR Value BZX84C15L SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 352 -128 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 1µ SYMBOL res 544 -128 R0 SYMATTR InstName R14 SYMATTR Value 4k7 SYMBOL res 192 80 R0 WINDOW 3 -254 -27 Left 2 WINDOW 0 -5 2 Left 2 SYMATTR Value R=100+sqrt(54000*V(Vin)) SYMATTR InstName R15 SYMBOL res 128 80 R0 WINDOW 0 -2 40 Left 2 WINDOW 3 -2 83 Left 2 SYMATTR InstName R16 SYMATTR Value 1k SYMBOL res 400 -32 R90 WINDOW 0 9 81 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 1k SYMBOL npn 48 208 R0 SYMATTR InstName Q7 SYMATTR Value 2N2222 SYMBOL res -96 -144 R0 SYMATTR InstName R12 SYMATTR Value 1k SYMBOL res 112 128 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R13 SYMATTR Value 10k SYMBOL cap -16 128 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 100p SYMBOL diode 0 320 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -17 25 Left 2 SYMATTR InstName D7 SYMATTR Value 1N4148 SYMBOL cap 448 -160 R90 WINDOW 0 27 65 VBottom 2 WINDOW 3 5 -6 VTop 2 SYMATTR InstName C5 SYMATTR Value 1n TEXT -320 -136 Left 2 !.tran 0 5m 0