I'm familiar with the configuration to make an LM317 (voltage regulator) into a current source. You connect a resistor between the Vout and Adj pins (Say 1.24 ohms) and draw the output directly from the adjust line (not the Vout line). With that resistance, you get a constant output current of about 1 amp. Easy peasy.

I'm trying to do that with an XRP29302. They are also linear regulators, but with some added bells and whistles. Instead of the 3 pins of the LM317 (Vin, Adj, Vout), it has 5 (Vin, Enable, Adj, Vout, Gnd). I tried hooking it up in a similar way, but it seems to be no go. (It works somewhat, but the output current is far too low.) I don't know what I am doing wrong. I think I have to incorporate the gnd in an appropriate way, but not sure how.

Some LM317 info is here: http://en.wikipedia.org/wiki/LM317

Some XRP29302 info can be found here: http://www.datasheetdir.com/XRP29302+LDO-Regulators


Yes it can be used as a constant current generator. With reference to the circuit: -

enter image description here

Take all the ground connections and group them together - this is now going to be the output voltage point for your load and the voltage across R2 (ADJ pin) will cause current regulation when this voltage is 1.24 volts. In other words if R2 is 10 ohms then 0.24 amps flowing into your load will be the current limit. R1 may be chosen to be quite low but the data sheet doesn't appear to say if this can be zero ohms. Maybe an experiment or more digging around will find an answer.

This method isn't limited to this regulator. Here's a 7805 regulator turned current source: -

enter image description here

| improve this answer | |
  • \$\begingroup\$ Thanks for the answer. It's given me some ideas to investigate further. I don't think R1 can be 0 ohms as the chip wants to maintain a 1.24 volt difference between the pins. \$\endgroup\$ – Jiminion Dec 7 '14 at 7:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.