SIMPLE DC TO DC CONVERTER 1

The DC to DC converter circuit below uses an N-mosfet to produce a variable output of 3V and above depending on your input voltage. The maximum output of the circuit will be little lower than the input voltage.

3A TO 5A DC TO DC CONVERTER CIRCUIT

 VARIABLE DC TO DC CONVERTER CIRCUIT EXPLANATION

 

Every mosfet is controlled by the level of voltage that enters its gate. The circuit above is a simple mosfet switch circuit. The more voltage the gate sees, the higher the voltage that will flow from Drain to source.

 R1 and U1 forms a variable voltage divider, whiles R2 reduces the gate current.  when input voltage is applied, the gate receives a divided voltage from R1 and U1 through U2. This voltage turns the mosfet on. As the mosfet turns on, part of the input voltage flows from drain to source and given as output. C1 serves as output filter. 

U1 is a 10k variable resistor. By adjusting it, the output voltage changes proportionally.  

U1 can be replaced by a fixed resistor of know value using a try and error approach.

 R1 is left as 10K for less than 24V input. Increase it by 10K or higher when handling voltages higher than 24V (two 12V batteries).

Any N mosfet will work. only make sure that its voltage rating is higher than your input voltage.