This inverter circuit can provide up to 800mA of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 75% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.

Schematic


Parts
R1, R4
2
2.2K 1/4W Resistor

R2, R3
2
4.7K 1/4W Resistor

R5
1
1K 1/4W Resistor

R6
1
1.5K 1/4W Resistor

R7
1
33K 1/4W Resistor

R8
1
10K 1/4W Resistor

C1,C2
2
0.1uF Ceramic Disc Capacitor

C3
1
470uF 25V Electrolytic Capcitor

D1
1
1N914 Diode

D2
1
1N4004 Diode

D3
1
12V 400mW Zener Diode

Q1, Q2, Q4
3
BC547 NPN Transistor

Q3
1
BD679 NPN Transistor

L1
1
See Notes

MISC
1
Heatsink For Q3, Binding Posts (For Input/Output), Wire, Board