### Author Topic: Digital Pot or Digital Regulator  (Read 2230 times)

##### Digital Pot or Digital Regulator
« on: December 19, 2014, 03:37:00 AM »
I am looking for a way to take 18V and digitally regulate it between 6 and 16V. My original idea was to use an arduino to control a digital pot in an LM317 regulator circuit but most digital pots I find have a small wiper current. I need at least 0.5A to be safe. Any recommendations on a digital regulator?

#### Digital Larry

##### Re: Digital Pot or Digital Regulator
« Reply #1 on: December 19, 2014, 11:02:37 AM »
Not that I've done this or anything, but I'd be tempted to try using a DAC output with a pass transistor to handle the extra current.  Since your DAC output is probably going to be below 5 volts you'd need an opamp running on the higher voltage and maybe some precision resistors to give you the right amount of voltage gain.

Google around to see if you can find anything like this.  I tried it but it was mostly articles talking about using regulated power supplies for audio DACs.

This is what I would call an "intermediate" project because you'll need to consider many things like the low current gain for power transistors, etc. and there are probably more things that could make it go south than I can think of.  Perhaps one of the more analog oriented brainiacs will chime in.
Digital Larry
DSP tinkerer and former transistor twister

#### g_u_e_s_t

##### Re: Digital Pot or Digital Regulator
« Reply #2 on: December 19, 2014, 01:40:58 PM »
the digital pot should work, you just need to get a nice high voltage one.  the AD5290 datasheet even shows an example of using the digital pot as a controllable powersupply.  the current going out the regulator can be up to 0.5A, but the current through the pot needs to be limited to 1mA or so.  if you use a 1k resistor between the output and the adjust pin, that should limit the max current to 1.2mA.  with a 10k pot in series with a 4.7k resistor, you would be able to swing the output voltage from 5.9V to 15.9V.

i keep thinking there must be some LED or motor controller chip that does this, but most of them are PWM, so not so great for keeping a nice DC voltage.

building your own high current DAC is also a good way to go, but might be more complicated.  you could use the PWM out of the arduino, lowpass it with a resistor and capacitor, and send it to an opamp to be ampified.  this could either be an opamp with a high power transistor in the feedback loop, or maybe an LM386 or other speaker driver amp would work.