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Most basic laser diode driver?

gigi2

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Is a simple LM317-based laser diode driver safe for powering a laser diode?

(the diagram is at 1:37)

I've been told the the proprietary drivers offer some extra protection from very short spikes (on power up and shutdown) in the current which laser diodes are very sensitive to and might be damaged from. But isn't the LM317 regulator taking care of that itself already?

I've been told this from people who actually sell commercial laser diodes so I'm thinking they might be showing some bias.
 

FireMyLaser

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LM317 regulator is fine for most lasers. It's just inefficient. It may requite heat sinking at higher powers. You'll know if it gets hot.
 

RedCowboy

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Remember to mount with an isolator.



NOTE: If you were to be running this on your desktop and you disconnected the load ( laser diode ) while in operation and then reconnected it without first disconnecting the battery, you could blow your laser diode.
 

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Benm

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Well, it is a design that works for lower currents, it's pretty hardy, and affordable, but that's all good things you can say about it.

The major downside are:

- Requires whopping 4.25 voltage drop to operate withing specification
- Must have significant output capacitance to ensure stable operation, risking destroying laser diodes with intermittent (i.e. any non-soldered) connections
- Electric contact between heatsinking tab and case causes problems as well illustrated above
- High heat dissipation in both the LM317 and current setting resistor and any serious power level

This circuit is fine if you want to test a laser diode running from a bench power supply or something like that. I would not recommend using it in actual pointers though, unless they are low power and you have -a lot- of voltage to drop between batteries and laser diode. If that is the case you'd probably be better off using a host that uses the appropriate number of batteries for the load.
 




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