The circuit above sets current
The circuit below sets voltage
Above
Lm741 or lm358 op amp
2 1k resistor, 1 68k resistor
1 1k pot, 1 .1 ohm resistor
1-2 irfz44n depending on load and heatsink.
1 5.6 volt zener diode to ground pin of op amp.
Below
Lm2596 dc-dc module to drive heavy loads.
The 3 amp module can drive 40 amp load
Add 2 Irfz44n and a 1 k resistor.
For large load add a cap and for inductive
Load and a diode.
