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Building Tiny DDL Driver

Wolfman29

Wolfman29

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]So I have taken it upon myself to build a tiny DDL driver, one that will (hopefully) fit in an Aixiz module. I know it's been done before, but I don't have the money to buy any. Haha. Anyway, so I have some questions, mainly concerning... where the falafel can I get parts?

Here is my circuit:

View attachment DDLcircuit.BMP

I have found that at Fry's Electronics, I can get 10Ohm chip resistors (will need three of these in parallel, not a huge deal), in order to get 3.333 Ohms which is about what I need to drive my red diode.

Now, what kind of capacitance do I need to protect my diode? I obviously need some seriously small caps in order to fit them into the Aixiz module correctly (probably I would have to use chip caps), but they don't seem to sell any chip caps with 10uF. Anyone know where I can find chip caps with that capacitance, or at least a bit lower than that so I can just stick a bunch of caps in parallel (like in the circuit) in order to achieve 10uF? Because I hear that 10uF is a good amount for a DDL driver.

Further, is there somewhere I can order an SMD LM1117 or LM317? My LM317 that I have right now is the large one and won't nearly fit in an Aixiz module... so any ideas?

Thanks, I appreciate it!
 





To Silvershot: I am going to make a keychain handheld, or at the very least, a small handheld with this driver.

To Prototype: USA, all the way (not really, I hate my country).
 
Digikey or Mouser should both have what you need and more, but not sure which would have the best price, but they both will almost assuredly have the parts.
 
Awesome. Just ordered a crap load of parts! Thanks! Will post a picture of the finished build once it's... finished?
 
Hey - if you're making a keychain sized laser, keep in mind that for an LM317 or LM1117 based build, you're going to need 2x lithium batteries (except maybe if it's a red laser, and you're using an LM1117)

That sort of kills the small form factor option :(
 
side note, with the surface mount regulator (317 / 1117 etc) & resistor(s) you're dealing with the same amount of heat dissipation as through hole versions but smaller components... you've probably already thought about this, but good thermal conduction to the host will help lots, if you're using an appreciable amount of power...
Pardons if I'm being captain obvious : )
 
Thanks for all the advice everyone. Not to be rude, but yeah, I was aware of the thermal conduction and the voltage drop out ;) Thanks though! Now I am sick though -.-
 
The voltage drop is variable though, and I think at diode diode currents it will be closer to 1V.
 
I just checked the datasheet and it says the dropout voltage only varies by .1 volts, an amount that the driver should easily be able to dissipate.

IOUT= 100mA 1.10 1.20 V
IOUT= 500mA 1.15 1.25 V
IOUT= 800mA 1.20 1.30 V
Click to expand...
 
Last edited:
The dissipated value will be the extra amount of power you push thru it.
Have you ever tried power a LM317 in a car battery? Yeah don't do it.
445 diode
4.5v 1.8A config

dissipated: 7.5v @ 1.8A = 13.5W

RHD tried to say that you can use lower voltages because any extras will be wasted in heat.

Oh sorry you already know the thermal conduction issues and etc. ~.~
 
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