circuit to pulse a laser diode, using a 555 and a 2n2222a

[semp]

Hello

I have been looking online for a circuit to pulse a laser diode, I have seen a circuit for high power diodes using a 555 and a 2n2222a to give up to 800ma.
What i really want to do is get power up to 1200-1300ma, I read somewhere its posible to run transistors in parallel, I thought I could connect two 2n2222a's by joining the bases together and the emitters together leading to the laser, and to stop either one of the transistors blowing, connect a 5.1 ohm 2watt resistor to each collector, which would give no more than 1200ma at 2v to the laser diode.

Does this sound like it will work? I dont really know much about electronics and I could be way off! I would just make it up and try it, if the laser wasnt so expensive and I dont want to destroy it by accident.

any one have any knowledge in this area?

 

[max0412]

Re: laser diode 555 circuit

Pulsed 1.2A is nothing for a single mosfet. You didn't say your duty cycle and operating voltages and frequency. You could probably use something like this.

http://www.fairchildsemi.com/ds/FD/FDN357N.pdf

Hard to say without specifics.

There are also numerous IR led driver circuits on the net (555 based) they also are pulsed at about 1 or 2A.

 

[semp]

Re: laser diode 555 circuit

The circuit would be 5v and laser is 2v. The duty would be under 10% I think, Im just going to triger single pulses when needed, and the pulse time would be in between 0.05 sec to 0.5 sec long, with at least a few seconds before the next pulse. May be a single 2n2222a will work fine for a duty cycle like this?
I dont know

 

[max0412]

Re: laser diode 555 circuit

Try this. First test the circuit using cheap suitably rated diodes ,if it works the way you want then use your laser diode. You may have to adjust the resistor value .You can check the current pulse by measuring the voltage across the emitter ballast resistor (I = E/R).

If your laser diode is out of the visible spectrum be careful you don't blind yourself!

Driving laser diodes reliably can get pretty complex are you sure a cheap IR led wont do what you want?

If you can you should use a logic level mosfet.

 

[semp]

laser diode 555 circuit

ok thanks, i will just make it and try with leds and check I get the right measurements from it

 

[FvM]

Re: laser diode 555 circuit

There are a lot of different laser diodes available, only a few are likely to stand the intended currents without beeing destroyed within microseconds...

 

[max0412]

laser diode 555 circuit

FvM is right are you sure your LD can handle the current pulses you plan on giving it? You are making the decision on the duration and magnitude of the pulse based on data sheet parameters I hope.

And use suitable rated rectifiers to test the circuit not LED's unless they are rated to handle the current and dissipate the power.