LM317 as current regulator and voltage regulator

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I am looking to build a driver for a laser diode and was wondering if it was possible to use a single LM317 to regulate both current AND voltage.

I have a 12V 1A switching PSU that I need to get down to 3.3-3.5V with a max of about 300mA. I plan to use a pot to drive current from around 50-100mA - 300mA, but the voltage needs to remain steady at 3.3-3.5VDC.

Currently this circuit will regulate the current:

http://i.imgur.com/tp7f5.jpg

This circuit takes 6VDC. Is there a way to get 12VDC down to 6VDC in this circuit without using an additional LM317?

If not, I assume I just add another 317 to get it down to 6VDC and input that without the need for anymore smoothing caps, considering it is a switching supply. Keep in mind that laser diodes are very sensitive to voltage and current fluctuations.

Thanks!

(x-posted to /r/askelectronics)

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Eisenstein

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Posted: 11 years ago
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