I am trying to control a current through several current-mirror device (specifically the
IREF pin on the TLC5940) using a single potentiometer. I've tried using a modified Howland current souce as in the following schematic:
While this works OK with resistor values as shown for dimming a LED, it doesn't work as a current sink given a 1.24V voltage source at the node marked sink. I am using an LM324 quad op-amp. If someone can suggest some avenues to explore for a voltage controlled I-sink, or voltage-controlled resistor (VCR), or an R-controlled resistor, etc. I would appreciate it. I'd like a minimalist circuit, if possible, as I'll need to control at least six current mirrors (TLC5940s) for my application, with a single pot/trimmer, and accuracy is not really critical in this application.
Some relevant links
- The question on voltage-controlled potentiometers is relevant, however, I would like to avoid buying a specialized part, if possible.
- People seem to have built VCRs out of photocells + LEDs, however, this seems a bit cludgey. I suppose an optocoupler is an option, however, I think linearity will be an (admitedly not huge) issue.