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Thread: Recommended transistor and base resistor for LED

  1. #1

    Recommended transistor and base resistor for LED

    Hi All,

    This is a very quick question with probably a very simple answer. What would a good transistor and base resistor be for driving a single LED from a Teensy 3.6?

    Usually I use a Darlington array ULN2003A when I have a few small things to drive from the Teensy which is simple and a straight connection to the Teensy pins. But in my current project, I have 8 LEDs to drive, all independent of each other. The Darlington array only has 7 outputs so rather than add another Darlington array that mostly is wasted in terms of space on the board and the actual array itself, I thought I could just use a single transistor with a base resistor.

    It is pretty much a bog standard LED with a maximum 20ma, but it does run from 12v on the positive leg and already has a current limiting resistor built in to it (itís essentially a push button switch with a built in LED that comes from the automotive world).

    All I need to do is switch it on/off/flash from a Teensy digital pin. Itís as simple as that, but I am not really used to using transistors that much and where I have, it has been snippets from already built circuits.

    I have been searching the forum and google and there are plenty of examples using FETs etc for driving LED strips, but I really donít have a case for that power or size.

    I could use a slightly bigger Darlington array, but the current one is already soldered to the board and works so donít really want to remove it and replace it.

    Many thanks in advance.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Nov 2012
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    20,692
    I’d start with a 2N3904 and 4.7K.

  3. #3
    Many thanks Paul. Much appreciated.

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