LM317 basic switch mode supply

Thread Starter

rbg5k

Joined Jan 26, 2010
5
You can set up an LM317 as a constant current supply with a simple power resistor between the output pin and adj pin to set current and take your CC output from the adj pin.

Now, if I wanted to also have a switch mode (and constant current) supply, can I simply switch the input voltage on/off at the LM317 input?

Say 100khz or so with an on/off pass transistor at the LM317 input?

And I suppose a choke on the output?
 

Thread Starter

rbg5k

Joined Jan 26, 2010
5
I know there are other. more suitable parts designed for smps but I have a bunch of boards with Lm317 already that I'd like to utilize.
 

SgtWookie

Joined Jul 17, 2007
22,210
There are a couple of schematics in National Semiconductor's datasheet for the LM117/LM317 on page 18. The "Low Cost 3A Switching Regulator" didn't simulate well; it just acted as a linear regulator.

Didn't try simulating the 2nd one.
 
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