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
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    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:

    [​IMG]

    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
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    Some kind of variable voltage regulator like the LM317?
     
  3. ErnieM

    Thread Starter AAC Fanatic!

    Apr 24, 2011
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    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
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    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

    Member

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