300mW laser driver

[lovelypotato]

Hello everyone, I am new to this forum.

I am currently having a school project that require me to build a laser engraver. I have done some research on laser diodes and laser drivers.

I have bought a LPC-826 laser diode(660nm 300-400mW Red Laser Diode).

So far I have did some simulation and did some testing by replacing the laser diode with LED and did some measurement of voltage and current across the LED.

However the output does not seems to be tally with what I have simulated and I am wondering what is the problem with it.

The simulation result

The voltage across the LED tested is however is around 6V and current across is around 160mA with a 9v as input. By calculating the power P=VI I would get around 960mW and I afraid it would burn my laser diode. I am wondering whether if it's the circuit design problem or any possible other reason that might be an issue and I would need some pros help here.

Besides that, does the circuit designed actually work with my laser diode? I have found the circuit online at many other websites that have a similar design.

Sorry for my English, I am from Malaysia and English is not my native language. Thanks in advance for anyone help! :yh:

**Edit: Besides that, based on the simulation result P=VI=3.65V*250mA=0.9125mW, am I suppose to change the resistance value and make the output to around 300mW?

 

[ChaosLord]

I'm not quite at driver design level, but you may want to try testing it with a test load instead of an led. The test load can be set close to the Vf of the laser diode, giving more accurate results.

 

[Tw15t3r]

Actual Optical Power is different from Electrical power. What you have calculated using P = VI is the electrical power input to the LED or the laser diode if you were to connect it. The laser diode is not 100% efficient, and so you will have to put in more than 300mW to get 300mW of optical power.

You don't need to worry about the electrical power input to the diode. What you must care about is the current rating of the laser diode that you have. Right now, the two 10 ohm resistors you are using in parallel are calculated to give 250mA of current (actual test results may vary). If your laser diode can be operated at 250mA, then it is ok.

 

[lovelypotato]

Actual Optical Power is different from Electrical power. What you have calculated using P = VI is the electrical power input to the LED or the laser diode if you were to connect it. The laser diode is not 100% efficient, and so you will have to put in more than 300mW to get 300mW of optical power.

You don't need to worry about the electrical power input to the diode. What you must care about is the current rating of the laser diode that you have. Right now, the two 10 ohm resistors you are using in parallel are calculated to give 250mA of current (actual test results may vary). If your laser diode can be operated at 250mA, then it is ok.

I have found this chart from some of the thread in this forum:

Based on this chart does that means that if I wanted to obtain somewhere around 250mW I'll have to make the input to be 370mA and 2.5V? Or do I only need to fulfill the 370mA case and voltage can be ignored? And what if the voltage goes too high?

I've also found these 3 chart from http://laserpointerforums.com/f50/lpc-826-graphs-63867.html#post913902 where it mention only the current that affect the power, so voltage value doesn't do anything to the laser diode?

Thanks a lot for your response

 

[Tw15t3r]

Yes, you just need to concentrate on the current. The voltage will tend to vary, because when the diode heats up, it could change. Just control the current and you will be fine, you do not need to worry about the voltage.

Yes, you have read the graph right, and you will need 370mA to obtain 250mW.

Good luck with your build!

 

[lovelypotato]

Yes, you just need to concentrate on the current. The voltage will tend to vary, because when the diode heats up, it could change. Just control the current and you will be fine, you do not need to worry about the voltage.

Yes, you have read the graph right, and you will need 370mA to obtain 250mW.

Good luck with your build!

I see. I think I've figured out what to do next. Thanks a lot for your help!! :thanks: