PWM control with a DDL circuit?

[Ch3fk0ch]

Hello,
i am new in the Laser section and an electrical noob (i am more a mechanical engineer)^^
I build myself one of the "DVD Laser engraver" with Easydrivers, Arduino Nano and a 1W 445nm Laserdiode.

As driver i used something like this:

Just that i add an Transistor E3055 at the GND to turn the Laser on and off.

Thats works fine but now i need an update. I will control the brightness of the Laser to engrave B&W pictures.

Is there a way to do it with that driver by adding a MOSFET instat of the Transistor or did i have to build a new driver (or buy one of the china ttl driver for 8$)?

I hope u can help me.

Thanks

(sorry for my english)

 

[lasersbee]

I'd go for the $8.00 solution...

BTW it would be nice if you introduced yourself
to the Forum in the Welcome section...

Jerry

 

[Ch3fk0ch]

So, there is no way to control this circuit with pwm over a Mosfet?

 

[lasersbee]

Try Googleing "constant current driver ttl control" or similar
search criteria...

Jerry

 

[Benm]

Using a transistor to short out the laser diode will work under some conditions.

It's not ideal since you will be dissipating power in the voltage regulator whevener the laser is off, but given sufficient cooling and no concern with power consumption that'd be okay.

One problem could be instability in the power regulator. As drawn there is capacitor at the output of the regulator, which will limit the speed at which you can turn the laer on and off. This capacitor is required to have stable operation of the LM317 though.

So yes you can blank this driver by shorting it out, but not at great speed and not with good efficiency.