DDL driver QUESTIONS

I believe it is an linear regulator driver using lm317 ?

but what does DDL stand for?

Also I read that DDL drivers can not modulate lasers fast, thinking above 10kHz. Is this true? if so why is that?

PS: what driver do fast modulating laser modules use?

Yes, the "DDL driver" is a simple current regulator probably directly derived from the National Semiconductors LM317 datasheet. It received its name because a member on this forum "Daedal" (hence "DDL") made a post about it as a simple and effective current regulation circuit, especially compared to simple current-limiting resistor circuits that were presented by people like Kipkay in his videos.

The LM317 circuit is actually pretty responsive, but the "DDL" circuit topology isn't designed for modulation, mostly because it lacks an input control. You can still perform modulation with a LM317 though; people have made LM317-based audio amplifiers before, and it could definitely be adapted for laser modulation. The only problem is that a DDL circuit depends on having a reference resistance in order to regulate current. To control this you'd need some input like a transistor, and if you're going to use that you might as well just directly modulate the current with the transistor itself.

Many "fast" modulation circuits exist. They usually just consist of a transistor that performs voltage-controlled current regulation. For example you can perform modulation with a circuit like this linear MOSFET dimmer circuit. Just vary the input voltage to the PWM pin (or use PWM if you want) and it'll change how much current is produced. I use it all the time for current-regulated experiments.

Benm also has a nice controlled laser driver that you can use.

You can also buy premade ones like Dr.Lava's Flexmod. It has some nice features like interlock, ESD protection, analog/TTL control, and all the tuning components that Benm's design includes. Of course that driver costs $40. I tend to just build transistor circuits for modulation.

(TTL = on and off; analog = variable output power)

For your green lasers, you'll simply have to buy a laser that has modulation built into its driver. Lasever's lasers have analog modulation and work quite well (good price too).

Finally, you can buy some of the drivers on eBay that are specifically made for modulation. Most are just TTL controlled however. They usually have buck drivers built in which is convenient, so you can plug them into a 12V+ source and they'll work (after tuning their voltage). For that price, you might as well just spend twice the amount for a Flexmod and get all the extra features.

Thanks very informative post,

so what kind of drivers do the cheap laser pointers on ebay use? They take three LR41 batteries or two AAA.

Does a laser module include the driver?
That is what I always assumed.

The drivers in cheap laser pointers usually use a dedicated or discrete linear driver that consists of an OP amp, and a transistor... it's more or less what's inside of an LM317, just discretely done. That and the plus of them is they have a considerably lower dropout voltage, so they can run IR diodes with only 3 volts.

Thanks,

Do laser modules, the ones with a case and two wires coming out have drivers inside?

See I thought that inside these laser modules there would a be a 3-pin laser diode and the driver circuit.

So are the driver circuits that Bionic-Badger mentioned, used to 'make' the laser module or 'drive' the laser module (which I assume already has a driver inside).

If someone could clarify this, it would be great.

Those LM317-based ("DDL") drivers are just for the plain laser diodes. Also green lasers almost always have their own driver because they have to do some feedback from the output.

If you see a module with wires sticking out, and it's not a green, you should first consult whatever info accompanied the module, and then see if there is a driver board. Sometimes the site will tell you what voltage to apply, and that often means there is a driver. Still, you need to verify.

Why are green lasers different?
I know they are made using DPSS but how does that affect the driver used?

I am currently looking to do some TTL modulation, I think the LM317 or similar driver would be ok but now am not so sure. I am talking about no more than 10KHz.

With the green laser drivers they do their own current regulation and many base it on feedback from the laser's output and other stuff. If you wanted to modulate that it'd be better to just modulate the input voltage source, not make a laser driver in the traditional (current limiting) sense. I'm not sure how such drivers will react. You might need to experiment.