Current Regulator: what is this part?

Discussion in 'General Electronics Chat' started by ErnieM, Sep 9, 2012.

  1. ErnieM

    Thread Starter AAC Fanatic!

    Apr 24, 2011
    I'm reverse engineering a low voltage LED I'm thinking of using, mostly just to see how it works. I've traced out the connections but one part escapes me.

    It is a SOT89 package with a top marking of "R113B." (searching that number leads nowhere). It is acting as a constant current limiter when across pins (2&4) to 3 it is given anywhere from 6 to 14 volts, where 14V is the highest I dare drive it. Here's how it appears in the schematic:


    A transistor typically has the emitter as pin 1, collector as 2 & 4, and 3 is the base, but neither an NPN or a PNP makes sense in this circuit.

    Is anyone aware of a current regulating part in this configuration?
  2. Markd77

    Senior Member

    Sep 7, 2009
    Some kind of variable voltage regulator like the LM317?
  3. ErnieM

    Thread Starter AAC Fanatic!

    Apr 24, 2011
    Something like that would work for this!

    However, the pinouts don't match a 317 and besides, a ref of 1.07V is out of spec for this. I also doubt any regulator would change the pinouts from a 317 anyway, engineer's being such a conservative bunch as we are.

    Close, very close. Good enough anyway. Thanks.
  4. panic mode

    Senior Member

    Oct 10, 2011
    unfortunately pinouts do differ, but circuit does look like classic LM317 when used as constant current source. pinout matches other regulators like LM2204
  5. BSomer


    Dec 28, 2011
    Perhaps what you are looking for is the CM7R250xxx. See attached...