DC- DC Converter 12V to 24V

This simple circuit is a DC-DC converter that converting up 12V source to a 24V. It can be used to run radios, small lights, relays, horns and other 24V accessories from a 12V vehicle with a maximum draw of about 800mA.

This DC-DC Converter can be used to charge one 12V battery from another, or step up the voltage just enough to provide necessary overhead for a 12V linear regulator. Using one op-amp as a squarewave oscillator to ring an inductor and another op-amp in a feedback loop, it won't drift around under varying loads, providing a stable 24V source for many applications. With a wide adjustment in output this circuit has many uses. 

Parts List

R1-R4,R7-R8 100K 1/4W Resistor 

R5 470 Ohm 1/2W Resistor 

R6 10K Linear Pot 

C1 0.01uF Mylar Capacitor 

C2 0.1uF Ceramic Disc Capacitor 

C3 470uF 63V Electrolytic Capacitor 

D1 1N4004 Rectifier Diode 

D2 BY229-400 Fast Recovery Diode See Notes

Q1 BC337 NPN Power Transistor 

U1 LM358 Dual Op Amp IC 

L1 See Notes 

MISC Board, Wire, Socket For U1, Case, Knob For R6, Heatsink for Q1

DC- DC Converter Notes 

1. R6 sets the output voltage. This can be calculated by Vout = 12 x (R8/(R8+R7)) x (R6B/R6A). 

2. L1 is made by winding 60 turns of 0.63MM magnet wire on a toroidial core measuring 15MM (OD) by 8MM (ID) by 6MM (H). 

3. D2 can be any fast recovery diode rated at greater then 100V at 5A. It is very important that the diode be fast recovery and not a standard rectifier. 4. Q1 will need a heatsink.