Powering Multiple Laser Diode/drivers

[DJ DoubleBass]

I'm continuing to put together parts for a multiple (low diode power) laser projector. (5mw diodes = no needed variances) These are cheap diodes that have a driver attached:

http://cgi.ebay.com/5mW-Green-laser-...item27abb05865

I'm planning on using this circuit for the diode/drivers:

http://www.photonlexicon.com/forums/...d.php?p=115439

NOW, to power that circuit, (called "Analogue Laser Tester") I was going to use a 9v 300ma regulated "wallwart" like this one:

http://www.allelectronics.com/make-a...GULATED/1.html

I wanted to double check my theory on this.

One 9v 300ma regulated "wallwart" to power one "Analogue Laser Tester" circuit....Would there be any problem with dialing it in at 3V 350ma (what the diode's specs call for) running 2 diode/drivers in parallel?

I just wanted to see if I could get just 3 Volts at 350ma even though the voltage regulator on that circuit is 5 volts.

I would run 3 but I think that would pull too much current from the "wallwart."

I'll be using momentary push buttons to flash the laser diode/drivers on/off. (switches will be between the driver and the "Analogue Laser Tester" circuit)

Thanks for any help

[Daedronus]

Depends on your diode driver, if it's linear, it will draw 350ma from the 9v supplay even if the out is 3v at 350ma. The difference is wasted as heat in the driver.

As far as I know it works like that.

[buffo]

How many modules are you going to have? Each one will be drawing 350 ma of current, so you need to know how many you'll have in total before you decide on a power supply. (Just add them up and multiply the total number of modules by .35 and you'll have your current draw in amps.) It's a good idea to size the supply to be at least 20% larger than you need. So if you have 10 modules (3.5 amps), then get a 4 or 5 amp power supply.

You don't need the analog tester circuit at all. It will not work for your application. It's designed to feed the low-current modulation inputs on lab laser drivers; it can't deliver enough current to power the modules you want to use. What you want is a 3 volt power supply that can source enough current to power all the modules directly.

If you can't find a suitable 3 volt power supply that will supply enough current, you'll need to buy a 5 volt (or higher) supply and then install a voltage regulator to reduce the voltage to around 3 volts to feed the modules. This is easily accomplished with an LM-317 voltage regulator package and a couple resistors, plus two filter caps. You can buy the parts at Radio Shack, even. (Though allelectronics will have them for a lot cheaper.)

If you need more than 2 amps total current, you'll need to install a pass transistor in parallel with the LM317. See this circuit for details. (Don't sweat it, it only adds a couple more components.)

Re: your theory... A DC voltage regulator will reduce the voltage only. It will not increase the current at the same time, like an AC transformer will. So if you need 3 volts DC at 4 amps, and you start with a 5 volt DC power supply, then that 5 volt DC power supply better be able to source at least 4 amps worth of current or it won't work.

Also remember that the voltage drop across the regulator will create heat that will cause the regulator to get hot. In high current applications, and especially in cases where there is also a large voltage drop across the regulator, a heat sink must be installed on the regulator to shed this heat.

Adam

[DJ DoubleBass]

Alrighty then. (redesigning)

So after reevaluating blah, I looked around for a beefy (er) 3V power supply to run all of the diode/drivers, which total 8. (8 x .35ma a piece = 2.8 amps of total power needed) I found this 3V 2.5A power supply for 10 bucks:

http://computerlogin.com/sales/produ..._5A_z_0049.php

The way this projector will be built will be in 2 halfs. (one half in each corner of the stage, with a single controller running both halves) Each half will house 4 diodes. I'm thinking of using 2 of those 3V 2.5A power supplies, one for each half. Since I'll only need 1.4 amps of power per half, 2.5amps of power should do the trick. (plenty of headroom)

The controller will be probably 20ft away from the halves, and I'll still use momentary push buttons between the power supplies and diode/drivers for control.

How does the new plan sound?

Anything I've missed?

Thanks again for everyone's help. VERY appreciated

[buffo]

The long wire run between the projector housings and the controller is going to be a problem. The voltage drop might be enough to prevent the lasers from working at full power.

There are a couple things you can do. The cleanest solution would probably be to use a transistor to turn on each module, and just sent a low current signal from the controller to the base of the transistor to turn it on. But that adds parts and complexity, which I think you said you wanted to avoid.

Another solution would be to go on E-bay and buy a beefy 3.3 volt power supply (like this one) and build it into the controller box. Then send the power from the controller through the switches and straight to the modules in the projectors. That makes the wiring runs shorter, since it's only got to run one-way (to the projector).

Even so, you'll have 350 ma running through 20 ft of wire. If you use #22 gauge wire, that's a little over .1 volts dropped, which is acceptable. (The drivers will handle the slightly higher 3.2 volt input just fine. Remember they're designed to be powered by batteries, and a pair of alkaline AA batteries can deliver 3.5 volts when fresh.)

Also, you need to make sure that with no load on the PSU the voltage doesn't drift up too high. Anything over about 3.6 volts is risky. You could blow one of the laser modules when you hit the momentary on switch. Worst case, if the PSU has a high idle voltage, put a small load on it (indicating light or something) to give it some base load to keep the voltage in check.

Adam

[DJ DoubleBass]

I LIKE THAT Powersupply! I should of checked ebay sooner. Shoulda known that ebay would have what I need

Thanks for chiming in Buffo. I figured that you would some time.

Could you chime in on my neighboring thread?

It's the one about "Using Piezo Elements To Control Lasers"

In a nutshell I'm gonna use one Piezo per drum for triggers, a popular thing to do in drum land, and they'll be one trigger per laser, one laser per drum. Each drum will trigger a different laser/effect.

Your opinion on that would be greatly appreciated

[buffo]

I looked into that thread earlier. It seems that several people were suggesting other methods of detecting the drum hits (microphones, etc) besides the piezo elements. This is good advice as far as I'm concerned.

Also, I'm not familiar enough with the sensors you were planning to use to really recommend a circuit based on them. However, like others, I question the wisdom of using a device that can generate several hundred volts (or more) as your sensor. It would seem that such a sensor would be more trouble than it's worth (especially considering that the rest of your electronics will be operating well below 12 volts...)

I think Jerry had most of the circuit figured out... I suggest you pursue his suggestions first. (He's more than qualified to offer advice regarding electronics projects.)

Adam