LASER Voltage/Current Requirements for PWM

[Cyparagon]

Without checking things prior to the PWM generator, looks good, except it looks like you've shorted the laser.

 

[rueffy]

PWM generator is fine, tested it prior. You mentioned in your post

(9V)---(resistor)---(laser+)---(laser-)---(FET drain)---(FET source)---(ground)

You've got the Laser + and Laser - next to each other, I too noticed it was shorted, I took it your list of components was a series list, starting at top to bottom.

 

[Cyparagon]

Assuming you have correct polarity, the resistor needs to be in series with laser which needs to be in series with the FET... as long as the FET's source is grounded.

 

[rueffy]

So what your saying is I should have the LASER negative connected to the source/ground?

 

[Cyparagon]

Just... remove the short.

 

[rueffy]

Thank you for your help thus far, I appreciate your continuous help.

Short removed, limited success, I had a very dull beam, wasn't bright enough to get the receiver up and going.

I've sat down tonight and come up with an alternative circuit, does it look viable?

My diodes requirements are:

Input Voltage: 2.4V
Input Current: 40mA

By incorporating a LM317, I can provide the fixed voltage input to the LASER diode of 2.4V, I would then have a MOSFET open and close the earth connection in sync with the PWM voltage applied to the gate. The current limiting resistor would be in series with the MOSFET. Would this actually work?

 

[Cyparagon]

So you've changed what "laser" is now? Describe/define/depict "laser" please.

 

[rueffy]

Yes, my other laser had seen a little too much experimentation. I have a LASER diode now. More information available if needed.

10mW Laser Diode
10mW laser diode component, red in colour and supplied with 7mm dia collimating lens.
SPECIFICATIONS
Threshold current: 24mA
Operating voltage: 2.4V
Operating current: 40mA
Optical power: 10mW
LD reverse voltage: 2V
PD reverse voltage: 30V
Size: TO-18 (5.6mm dia)

 

[Cyparagon]

In that case, just power it from 12V and use a 240 ohm (or slightly over) for the current limit. That should put you at just under 40mA. It is also a good idea to have a small value ceramic cap permanently across the diode. 0.01µF or something like that. If that is still too slow, add a ~330 ohm across the FET. This will put a bias current through the diode, allowing it to turn on faster.

 

[rueffy]

Thank you to all those that helped contribute to the development of my circuit (particularly Cyparagon). The project is now fully functional and I've made a video as part of my presentation to a class, the video shows the system in operation with a full description of signal flow etc.

http://www.youtube.com/watch?v=CCAkpJ-jG6A

rueffy.