cannot decipher datasheet's circuit example

Discussion in 'General Electronics Chat' started by tpny, Oct 3, 2012.

  1. tpny

    Thread Starter Member

    May 6, 2012
    Attached circuit is from lm317 datasheet. It's an example for a 6V 0.6A charger. I understand how it is 6V but I don't understand how the 1ohm resistor in the configuration makes it 0.6A limiter. Please help! Thanks!
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    The Vbe of the transistor is 0.6v, when the voltage drop on the 1 ohm resistor reaches this level the transistor will start to turn on, reducing the output current via the ADJ pin.

    This trick is often used in current limiting circuits, it's not very accurate due to the variability of Vbe, but it works.
    tpny likes this.