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Laser diode driver question Answered

I'm planning on building an on building an IR light source for a DIY night vision setup. to do thus I'm using a 300 mw IR laser diode. the diode needs to be powered by 2.2 volts. I'll be using a LM317T to adjust to voltage but my question lies in the current needed. I'm familiar with powering LED's but not with diodes. since the power is 300 mw and the voltage is 2.2 V would i be powering it using about 130 mA? in addition to that how would I achieve this? I know the LM317 can be used as a current regulator but how is this done? any help would be appreciated, thanks.


Here's a circuit, for 317 in current control mode, and the maths to work out your values.


Copy of maths.jpgtrimmable current source.JPG

Steve has a nice circuit.

The answers to your questions are as follows:

1. a diode is a diode. Whether that's a common "light emitting diode" or a laser diode ( a special subset of LED).

one thing to be careful of when using IR laser diodes is that they can hurt your eyes and are invisible to our range of sight

Another thing is to be careful about over temperature conditions, which can damage or otherwise render inoperable your laser diode. Many commercial drivers employ a temperature sensing feedback loop to avoid over-temperature conditions.

2) yes, 130mA, IFF the laser diode is driven by a constant-current source like the one Steve has shown in his reply.

Again, you do ideally want to monitor the case temperature to avoid exceeding its maximum temperature when driven at full power, especially if the device is mounted in such a way that heat cannot be dissipated well.

3) Steve said it well, although I would suggest that you consider keeping your operational current below the maximum unless you have employed a *solid cooling method to the completed assembly and are using some form of temperature feedback and/or safety shutoff.

Yes, when it really matters, temperature stabilisation stops the diode frequency wandering too.


I suppose it would really matter if the OP doesn't want to burn out a laser diode unnecessarily. A simple threshold detection scheme with a cutoff is no big feat, and it's SOP, just as applying a fuse or circuit breaker to a power supply would be. Considering that virtually all laser diodes come with warnings about exceeding temperature ratings, that's just common sense, wouldn't you agree?