This is my contributions to the already going thread on a 100 volt capable DC-DC buck boost using a 555 and a zener for regulation that uses the minimum parts. I don't even have a timing cap in there.
Set R1 for the Max I you need as the load and the zener will suck up what you don't use to maintain a constant voltage.. Of course this type of boost is only good if your load constraints are not all over the place.
Replace R1 with a PNP current sink that can be reversed bias with a feed back regulator and you can have a large output unit with low stand by current, instead if using a Zener like I do with low current demands
Version 4 SHEET 1 880 680 WIRE -128 -80 -256 -80 WIRE -112 -80 -128 -80 WIRE 320 -80 -112 -80 WIRE -256 -48 -256 -80 WIRE 432 -32 0 -32 WIRE -112 32 -112 -80 WIRE 320 64 320 -80 WIRE 320 64 304 64 WIRE 336 64 320 64 WIRE 432 64 432 -32 WIRE 432 64 416 64 WIRE 464 64 432 64 WIRE 464 96 464 64 WIRE -112 128 -112 112 WIRE -112 128 -208 128 WIRE 0 128 0 -32 WIRE 80 128 0 128 WIRE -112 144 -112 128 WIRE -32 192 -48 192 WIRE 80 192 48 192 WIRE 432 192 432 64 WIRE 432 192 304 192 WIRE 464 192 464 176 WIRE 528 192 464 192 WIRE 608 192 592 192 WIRE 464 208 464 192 WIRE 608 208 608 192 WIRE -112 256 -112 240 WIRE 80 256 64 256 WIRE 400 256 384 256 WIRE -208 320 -208 128 WIRE 384 320 384 256 WIRE 384 320 -208 320 WIRE 464 320 464 304 WIRE 608 320 608 272 FLAG -256 32 0 FLAG 80 64 0 FLAG 608 320 0 FLAG -128 -80 P+ FLAG 64 256 P+ FLAG 464 320 0 FLAG -112 256 0 SYMBOL Misc\\NE555 192 160 R0 SYMATTR InstName U1 SYMBOL voltage -256 -64 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 10 SYMBOL res 432 48 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 250 SYMBOL ind 448 80 R0 SYMATTR InstName L1 SYMATTR Value 1mh SYMATTR SpiceLine Rser=0.1 SYMBOL zener 528 208 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 52 118 VBottom 2 SYMATTR InstName D1 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 592 208 R0 SYMATTR InstName C1 SYMATTR Value 1µf SYMBOL npn 400 208 R0 SYMATTR InstName Q1 SYMATTR Value 2N5550 SYMBOL npn -48 144 M0 SYMATTR InstName Q2 SYMBOL res 64 176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 1200 SYMBOL res -128 16 R0 SYMATTR InstName R4 SYMATTR Value 1200 TEXT -240 360 Left 0 !.tran 0 0.010 0 0.01 startup
Jamie