jakehop

Hi Jack, thanks for your reply! I am having a hard time of conceptualizing your idea. However, the circuit that I am looking to integrate this solution into already has a negative voltage source, that I would just need to attenuate. It's like -80-90V, that I'm looking to get down to -50-25V. I would like to get some linearity. My digital potentiometers can't handle this voltage, and I was hoping to get some kind of solution that made use of the 8bit D/A's in my pic, so I could get a resolution of, say, 0,1V in that 25V of potential. Is this impossible? I'm currently working with a optoisolator, however it's not nearly as linear as I could hope for, even though the manufacturer claims exactly that!

Hi guys, I'm new here at the forum, and I've been searching for a solution to my problem without any luck! I need to design a circuit, where I can control a negative voltage with a PIC (in this case, the AT-platform). I've got the PIC's PWM-function, as well as digital potentiometers to control the circuit. However, the PWM is limited from 0-5V+ DC, and the digital potentiometers have certain limits to the voltage at their taps. The negative voltage should be -25 to -70 Volts DC. -50 Volts will also be OK if -70 is totally out of the question. So far, I've got a opamp working as an inverting amplifier, but even the best rail-to-rail model can only give me -22 volts from the +5V sources that I have. I thought about having the opamp controlling an elevated LM337 to get the -25V to -50V, but I can't get it figured out in my head, as I constantly bump into the limits of the PIC or the digital potentiometers. Also, linearity is important for me. The PWM allows me a resolution of 8 bits - 256 steps. If this proves a problem, I'll use a DAC to get 1024 steps. Does anyone have a clue as to how I can solve this? Kind regards, Jake