12V To 24V DC-DC Converter Circuit

This simple DC-DC converter can provide up to 24V from a 12V source. 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. It 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.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2, R3, R4, R8, R7 6 100K 1/4W Resistor R5 1 470 Ohm 1/2W Resistor R6 1 10K Linear Pot C1 1 0.01uF Mylar Capacitor C2 1 0.1uF Ceramic Disc Capacitor C3 1 470uF 63V Electrolytic Capacitor D1 1 1N4004 Rectifier Diode D2 1 BY229-400 Fast Recovery Diode See Notes Q1 1 BC337 NPN Power Transistor U1 1 LM358 Dual Op Amp IC L1 1 See Notes MISC 1 Board, Wire, Socket For U1, Case, Knob For R6, Heatsink for Q1

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.