I recently acquired some surplus 2:1 ADSL/ISDN transformer thingies, and was thinking about circuits they could be used in. I came up with the following circuit (LTSpice netlist follows) where a microcontroller could use one of them to generate its own supply voltage from a single AA/AAA cell.
Q3 and its associated turns act as a blocking oscillator to initially boost the voltage on the right hand side of L4, allowing a microcontroller to start up. The uC would then apply a square wave to R5, driving L1 and L4 to produce ~3.5-4 volts at the anode of D2. Once the voltage comes up, Q1 and Q2 shut the blocking oscillator down.
I thought it was kind of cute, though I don't know what practical application it would have, as charge pump voltage converter ICs that work from 1.5 volts are only about 50 cents. It also fails to start up if C2 is too large.
Version 4 SHEET 1 1260 836 WIRE 736 -144 -528 -144 WIRE 528 -32 -336 -32 WIRE 736 -32 736 -144 WIRE 736 -32 624 -32 WIRE -528 48 -528 -144 WIRE -496 48 -528 48 WIRE -384 48 -416 48 WIRE -336 48 -336 -32 WIRE -288 48 -336 48 WIRE -176 48 -208 48 WIRE -496 160 -528 160 WIRE -384 160 -336 48 WIRE -384 160 -416 160 WIRE -336 160 -384 48 WIRE -288 160 -336 160 WIRE -128 160 -208 160 WIRE 0 160 -64 160 WIRE 112 160 112 112 WIRE 112 160 0 160 WIRE 224 160 112 160 WIRE 432 160 224 160 WIRE 224 208 224 160 WIRE 432 208 432 160 WIRE -528 240 -528 160 WIRE 304 272 272 272 WIRE -304 288 -464 288 WIRE -176 288 -176 48 WIRE -176 288 -224 288 WIRE 736 288 736 -32 WIRE 304 304 304 272 WIRE 576 304 576 32 WIRE 0 336 0 160 WIRE 112 336 112 160 WIRE -336 352 -336 160 WIRE 432 352 432 288 WIRE 432 352 336 352 WIRE 512 352 432 352 WIRE -736 400 -944 400 WIRE -496 400 -656 400 WIRE -400 400 -416 400 WIRE -944 432 -944 400 WIRE 224 432 224 288 WIRE 432 432 432 352 WIRE 336 448 336 352 WIRE 0 656 0 400 WIRE 112 656 112 400 WIRE 224 656 224 512 WIRE 336 656 336 512 WIRE 432 656 432 512 WIRE 576 656 576 400 WIRE 736 656 736 368 WIRE -944 672 -944 512 WIRE -720 672 -720 448 WIRE -528 672 -528 336 WIRE -336 672 -336 448 FLAG 736 656 0 FLAG 576 656 0 FLAG 432 656 0 FLAG 336 656 0 FLAG -528 672 0 FLAG -336 672 0 FLAG -944 672 0 FLAG 0 656 0 FLAG -720 672 0 FLAG 112 112 Vcc FLAG -672 448 Vcc FLAG 112 656 0 FLAG 304 304 0 FLAG 272 224 Vcc FLAG 224 656 0 SYMBOL pnp 528 32 R270 SYMATTR InstName Q1 SYMATTR Value 2N2907 SYMBOL pnp 512 400 M180 SYMATTR InstName Q2 SYMATTR Value 2N2907 SYMBOL voltage 736 272 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 124 Left 2 SYMATTR SpiceLine Rser=1 SYMATTR InstName V1 SYMATTR Value 1.5 SYMBOL res 416 416 R0 SYMATTR InstName R1 SYMATTR Value 220k SYMBOL res 416 192 R0 SYMATTR InstName R3 SYMATTR Value 47k SYMBOL cap 320 448 R0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL ind2 -512 64 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 4 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 400µH SYMBOL ind2 -192 32 R90 WINDOW 0 4 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName L2 SYMATTR Value 400µH SYMBOL ind2 -400 144 R90 WINDOW 0 4 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName L3 SYMATTR Value 100µH SYMBOL ind2 -304 176 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 4 56 VBottom 2 SYMATTR InstName L4 SYMATTR Value 100µH SYMBOL npn -464 240 M0 SYMATTR InstName Q3 SYMATTR Value 2N2222 SYMBOL npn -400 352 R0 SYMATTR InstName Q4 SYMATTR Value 2N2222 SYMBOL voltage -944 416 R0 WINDOW 3 -305 -50 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value PULSE(0 3.3 0 110n 100n 0.000005 0.00001) SYMATTR InstName V2 SYMBOL res -400 384 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL schottky -128 176 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value 1N5817 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap -16 336 R0 SYMATTR InstName C2 SYMATTR Value 1µF SYMBOL res -208 272 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 68k SYMBOL sw -752 400 R270 SYMATTR InstName S1 SYMBOL zener 128 400 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -38 -70 VRight 2 SYMATTR InstName D1 SYMATTR Value BZX84C6V2L SYMBOL sw 224 304 R180 SYMATTR InstName S2 SYMBOL res 208 416 R0 SYMATTR InstName RLoad SYMATTR Value 470 TEXT -992 184 Left 2 !.tran 0.1 startup TEXT -984 120 Left 2 !K L1 L2 L3 L4 0.99 TEXT -984 152 Left 2 !.model SW SW(Vt = 2.7 Vh=-0.5)