12V To 24V DC-DC Converter Circuit

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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

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

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).

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.

Q1 will need a heatsink.

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Comments

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skywriter 12V To 24V DC-DC Converter Thursday, November 19, 2009 1:02:12 AM

It seems the circuit above is wrong. Q1 would never open because there is no difference of potentials between base and emitter

anonymous 12V To 24V DC-DC Converter Sunday, October 18, 2009 6:20:00 PM

Any specs on the inductor? For example if I wanted to buy one instead of making one? Thanks

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skywriter	12V To 24V DC-DC Converter	Thursday, November 19, 2009 1:02:12 AM
It seems the circuit above is wrong. Q1 would never open because there is no difference of potentials between base and emitter
anonymous	12V To 24V DC-DC Converter	Sunday, October 18, 2009 6:20:00 PM
Any specs on the inductor? For example if I wanted to buy one instead of making one? Thanks