PWM drivers for lasers. Why/why not?

[ossumguywill]

The MicroBoost does have PWM input control capability.. accepts modulation to 10kHz I believe. PWM input requires a small modification to a trace on the driver.

Is there a tutorial somewhere? The datasheet I have doesn't mention this. I sure would like to put PWM in my 445 though

 

[Xplorer877]

What are you going to use that rgb laser for anyway?

If its for a scanner, PWM isn't likely to be desireable, as it will give a dotted-line-appearance in the projection, unless your pwm is extremely fast (several MHz range).

The dotted line effect is what I want. By adjusting the frequency and duty cycle for each color I can adjust it so the that frequency is in phase with the one cycle of the turning mirrors to make a moving line effect. The duty cycle will affect the lenght of the line as it travels along the pattern generated by the mirrors. It's just a simple little projects I'm messing around with, not a sophisticated scanner.

Also Xplorer877, what power source are you using that won't freak out when you use fast PWM like that? I think both constant current and switching drivers HATE it when you use PWM.

My LM317 drivers are working fine with PWM.

-Tony

 

[ossumguywill]

My LM317 drivers are working fine with PWM.

-Tony

what frequency of PWM?

 

[Xplorer877]

what frequency of PWM?

Not sure, it's variable. But probably a few Hz to a few kHz. Smoothing caps before the switching transistor help keep the LM317s running fine.

-Tony

 

[Xer0]

Is there a tutorial somewhere? The datasheet I have doesn't mention this. I sure would like to put PWM in my 445 though

Yeah! please! show us!

 

[Benm]

The dotted line effect is what I want. By adjusting the frequency and duty cycle for each color I can adjust it so the that frequency is in phase with the one cycle of the turning mirrors to make a moving line effect. The duty cycle will affect the lenght of the line as it travels along the pattern generated by the mirrors. It's just a simple little projects I'm messing around with, not a sophisticated scanner.

My LM317 drivers are working fine with PWM.

If that is what you want, why not just do so by introducing the desired blanking for each color in the ilda frames?

In case you want to do it by hardware, i guess its feasible to create the pwm such that it matches a certain delay from the mirror movements, also resulting in the same visual effect, but that would be much more complex in terms of electronics required.

As far as LM317 drivers and PWM go: the lm 317 was never designed to serve in this application, but it can very well work. I've even seen people using 317's as amplifiers for HF radio transmitters (think in the several-100-kHz range). Such operation is beyond anything the designers ever intended or the manufacturers will guarantee to work, but that doesnt mean it won't in some occasions.

 

[LSRFAQ]

Put a optical pick off on the spirograph wheel, and use that to reset a 494 or 3525 PWM chip, or a couple of 555 monostables. I assure you you'll very happy with 1-2 khz or so PWM and some sync.

I can say this with confidence because I own a analog abstract console, I may do my stuff with a Xy galvo pair instead of spinning mirrors, but the concepts and frequencies are similar. Its still sine and cosine.

Your trying to do a "snake" or "Baton" effect.

Steve

 

[Xer0]

Still waiting for the shematic of drlava, where to change a trace for PWM

 

[ossumguywill]

Still waiting for the shematic of drlava, where to change a trace for PWM

lol yep... perhaps if we had some part numbers? My guess is it has to do with that 6-pin IC.

 

[drlava]

Hi, ok the instructions are --> HERE <--.

Note that this also allows you to use a low current switch to turn the driver on and off via the TTL control, without worrying about burning up the contacts on a clicky switch when you switch all the current on and off.

Also note that although it will appear dimmer, the eye damaging capability of the beam will not have decreased much, as it does when it is dimmed via analog means.

 

[ossumguywill]

Thanks a ton

 

[Benm]

How does it fare at projector speed modulation - say 10 kHz or so?

 

[Benm]

Well, what would be the problem with that? I dont see any difficulty in building a pwm capable current source running at 1.2 amps, or 12 amps for that matter. Questions remains is what its use would be.

 

[ossumguywill]

Well, what would be the problem with that? I dont see any difficulty in building a pwm capable current source running at 1.2 amps, or 12 amps for that matter. Questions remains is what its use would be.

A 445 diode, of course! I now realize I should have elaborated what "it" is lol.
I'm working on some flashlight PWM code as we speak, just tweaking to make sure it stays under 10khz. Maybe if it works I'll stick it in my 18650 kit.

 

[Xer0]

OK... and whats the maximum Frequency it could do?

 

[FireMyLaser]

Well, what would be the problem with that? I dont see any difficulty in building a pwm capable current source running at 1.2 amps, or 12 amps for that matter. Questions remains is what its use would be.

I believe that modulating high currents will cause huge inductance in the wires and driver which might corrupt the modulation and/or cause other problems.