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cannot decipher datasheet's circuit example

tpny

Thread Starter

tpny

Joined May 6, 2012
220
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!
 

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Sensacell

Sensacell

Joined Jun 19, 2012
3,448
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.
 
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