Dim a laser diode?

[MrMcChicken]

Hi all, I am going to bouild this easter an RGB laser. I want to put there potentiometers inside, for mixing the colors. So I could get all colors of the rainbow ^^. Now I have build a circuit with a lm317. This would be the " powersupply" for the laser. I want an input of about 12V, so i use lm317 to get a lower voltage.
I have put there an 10k potentiometer in. Now I can regulate the voltage between 3,9 an 3,3V. Would it be possible to dim a module with this? The module has already a driver.

 

[DrSid]

laser diodes need constant current driver. If there is already one, changing its input voltage would do nothing. If you provide enough, it will provide enough current for the diode .. if you don't provide enough, it will simply not work. You need current supply with regulation, and current ranges specific for every color - as it will be different for every color.

 

[Wytry]

It's hard to make a regulated driver with lm317 (or any regulator of this kind). You would need to get power potentiometer like 5 ohm, wich is rare. I recommend making driver of different type.

 

[MrMcChicken]

Okay, but i have no idea how to dim it else. Could i put a strong poti just beforte the driver?

 

[Wytry]

I see 2 options here:
- Use different driver that will let you control current with a pot e.g http://c4r0.elektroda.eu/_hv/lasers/dvd_sch.png
- Keep your lm317 driver (I dont know is yours correct but it should regulate current, not voltage, so you should connect it like this) of course you have to choose R1's value proper for your LD. Then add simple PWM modulation e.g MOSFET and uC.

I'd choose option #2 as it gives you more possibilities.

Edit:

The module has already a driver.

Sorry, I didnt notice it. I thought you were going to power LD directly. Could You take a photo of this driver?

 

[MrMcChicken]

I don't really understand what you mean. Should I use a potentiometer before the lm317 driver?

There won't be a driver before the diode. Sorry, first i wanted to buy one with a driver, but then i found drt's shop. So there wont be a driver already.

 

[MrMcChicken]

I don't really understand what you mean. Should I use a potentiometer before the lm317 driver? (opinion 2)

There won't be a driver before the diode. Sorry, first i wanted to buy one with a driver, but then i found drt's shop. So there wont be a driver already.

sorry for the double post. I am a bit in trouble with my mobile device.

 

[Wytry]

To choose driver I need to know what diode are you going to use.

 

[MrMcChicken]

A 1W m140 diode, and a 300mw Mitsubishi diode

 

[Wytry]

What about green? Are you going to use it in a projector?

 

[MrMcChicken]

The green one will be 85mW out of a pointer. No, it will be a handheld rgb.

 

[Wytry]

So you need 3 drivers, one for each color. I'd use there 3x STCS2 chip and dim each one with PWM. As PWM generator you can use ne555 or (if you have programmer) uC like ATmega.

Here you have schematic: http://laserpointerforums.com/f67/looking-stcs2-based-driver-schematic-71969.html to dim this driver you just need to apply pwm signal to stcs2's pwm input.