So I've recently been asked to see if I could come up with a simple solution to making a crude microprocessor controlled voltage supply.
I have a resistive heater that I need to control with a micro-controller. The heater has a resistance of 5-20 Ohms depending on how warm it is, and I need to supply it with less then an amp (typically ~0.5A, but I'd like to leave myself some wiggle room). I figure I need to supply it with 3-20V DC, and would like to work off a 24V DC supply. I also need to sense the voltage and current being supplied to the heater, on the order of once a second.
I figure that the voltage and current sensing are easily enough accomplished with an ADC and a voltage divider (for voltage) and a low-side shunt resistor (for current).
My concern is finding a simple design for a power supply that I can control with a micro-controller. The idea I've had is to use a high current adjustable linear regulator (like a LM338) where I use an op-amp in place of the rheostat. I figure if I configure the op-amp to be a 6x non-inverting amplifier I can then use the micro-controller to run a 0-5V DAC into the op-amp. I can then feed the output of the op-amp through a resistor into the LM338's "adj" pin. I only need to go down to 3V (0.5A at 6 Ohms) so I can tolerate a non-rail-to-rail op-amp and the voltage drop across the resistor won't be a problem.
So, before I go and order parts, can anyone see potential problems with this? A quick spice simulation suggests that it would work but I figured I'd throw it up for the experts.