DIY Homemade laser diode driver

Rad86N · Jul 8, 2009

rog8811 said:
...so only 2.5v for the laser diode?....

how did you get this number?

I confirm it. And the max current is 270mA or so.. measured
thats why i dont use the 5ohm resistor.. to get as much as possible from the 5V input. *even with the 5ohms, i could have burned matches with 16x dvd diode
i think, its maybe not as much mW, but at least longer life for the diode.

rog8811 said:
1N4007 should be OK, just measure the voltage drop over one of them to see that it gives you 0.7v

1N4007 drops 0.33V.. but i use it instead of - 1N4001 rectifier diode (protects LD if batteries are inserted the wrong way round).. i dont use it for the test circuit.
---
btw.. i tried 6x1.5V AAAs with the default DDL circuit as it is shown in the first post of this topic, and i burned the diode. i thought i can supply the driver with any voltage up to the LM317T max input and the chip will turn the unused power into heat.. but 9V demaged my diode. it just went dimm.. not even as bright as 5mW diode

i got the dvd drive with this diode for like $5 so please dont comment i killed a diode

not A diode yet.. lol

thanks for answers and/or any reaction.

rog8811 · Jul 8, 2009

how did you get this number?

Can I suggets you go to the laser driver page of my website, it gives all of the important info on the LM317 driver circuit.... you will then see where I got the number from.

I confirm it. And the max current is 270mA or so.. measured

That will be because the LM317 is not regulating... because of what I alude to above.

i thought i can supply the driver with any voltage up to the LM317T max input and the chip will turn the unused power into heat.. but 9V demaged my diode. it just went dimm.. not even as bright as 5mW diode

It was not the voltage that killed it..... it was the current.

Look, it may seem I am being difficult here but you seem to have missed one of the most basic shortfalls of the LM317 (it does not make it a bad driver though), I want you to find it out for yourself, I have refered you to the easiest place to find this info above.

Regards rog8811

dr-ebert · Jul 8, 2009

If you want to know about the characteristics of an electronic component, just check the datasheet. The 1N4001 and 1N4007 differ only in their reverse voltage tolerance - the 1N4001 can stand 50V while the 1N4007 can stand 1000V.

All standard silicium rectifier diodes have a voltage drop of ~0.7V (actually this depends on the current, it's 0.85V at 300mA). Germanium and Schottky diodes have 0.3..0.4V, however they're used only in special occasions.

Also according to the datasheet, an LM317-based constant current driver should drop not quite 3V (even if most people here say 2.25V, which would be true for the LM1117). You don't say what your power source is - how stable is it? Anyway it looks to me like your driver is out of regulation due to lack of input voltage, that's why you're getting too low current and think you don't need the 5 Ohm resistor - and why, with 9V, it then fried your diode.

Edit: ups, sorry rog8811, looks like I gave the answer away...

Rad86N · Jul 8, 2009

thank you dr-ebert
-and my power source is usb connector.. or 4xAA rechargables..
with 16x diode it gave me 2.43V and 130mA, which was enough to burn the black tape and light matches..

and btw i used the 5ohms when i was experimenting with those 9V of input voltage.

rog8811 · Jul 8, 2009

4xAA rechargables

What voltage? Standard rechargable AA are 1.2v.....

and btw i used the 5ohms when i was experimenting with those 9V of input voltage.

If we had been told that it may have changed the diagnosis, do you have a capacitor in the circuit, if so did you short it out before conecting the LD?

Edit: ups, sorry rog8811, looks like I gave the answer away...

...accidently, of course as you posted at the same time as me

Regards rog8811

Rad86N · Jul 12, 2009

nevermind.. thank you for your comments.. problems solved

i have a 47uF/35V cap in the circuit.. but i never shorted it out. when exactly is it recommended to short the cap out?
the cause of the LD death must have been the cap, because im using 9V now and everything works as it should.. no other LDs killed.
yesterday i changed 2x10ohms with 4.1ohm resistor.. which means max current output is some like 305mA .. now i wonder if this will be enough for the 22x dvd laser.. 3V and 300mA make almost 1W of power consumed by the LD.. i found some tables and graphs, but to make heads and tails off of thos.. mmh.. sry for my english

dr-ebert · Jul 13, 2009

My recommendation is to just throw out the capacitor (and diode).

Typical current for the LPC-815 LOC diode (which I think is a 22x) is ~420mA (3 Ohms).

changeup · Jul 13, 2009

Hi Daedal,

I set up the small breadboard like you were showing. For some reason, the only way I can get the pot to work is to ground one of the wires coming OUT from it. Any ideas....? Thanks

changeup · Jul 13, 2009

changeup said:
Hi Daedal,

I set up the small breadboard like you were showing. For some reason, the only way I can get the pot to work is to ground one of the wires coming OUT from it. Any ideas....? Thanks

I know this isn't a basic electronics forum,..............................
I also build 1/10th scale high powered electronic RC jets pulling nearly 80A on a 8000mA battery packs. Pretty fun, so I have an idea on electronics. It's probably right here in front of my mug. I guess I'll have to stare at it for awhile longer.

rog8811 · Jul 13, 2009

It is unlikely that Daedal (DDL) will answer this so I will have a go..

Could you put up a photo of what you have built, a nice clear one, then we may be able to help you out. If you are needing to ground the pot you have something set up wrongly, have you checked to see if the ref voltage is correct? (measure between out and ref, reading should be 1.25v)

Regards rog8811

oldscooliron · Jul 14, 2009

@ changeup I build RC stuff too! check out my website in my profile. I just got into helicopters last year. Do you have a link to your stuff? Sorry I can't help as I'm new to this too.

@ rog8811 or anyone else who knows!

Is there a way to up the mV/ma output of the "DDL Driver" so you can go more then 250ma? I'm using 2 - 10 ohm resisters now.

Is there a better lens I could get for my dvd LD? Here is the housing I bought:

650nm 5mW laser module.3.2V to with lens 650 nm OEM - eBay (item 360166159578 end time Jul-05-09 18:42:34 PDT)

Also what kind of ball park figure for mw are we talking with 250ma to 450ma? Will it be under 500mw?

rog8811 · Jul 14, 2009

Is there a way to up the mV/ma output of the "DDL Driver" so you can go more then 250ma? I'm using 2 - 10 ohm resisters now

All you need to do is use a lower value resistor. On the laser driver page of my website (link to site below) is a section on calculating the resistor for a specific output.

Regards rog8811

oldscooliron · Jul 14, 2009

@ rog8811

So if I want 400ma I'd need 3.125 ohm resistor?

Why is it my laser will burn black but no other colors?

rog8811 · Jul 14, 2009

So if I want 400ma I'd need 3.125 ohm resistor?

If that is what the sum gives you, yes... realistically use 3 x 1ohms in series and you will be close enough.

Why is it my laser will burn black but no other colors?

There is another current thread discussing this very subject, I cannot remember what the title or forum was, try search.

Regards rog8811
Edit, as I happened upon it again, here you go
http://laserpointerforums.com/f51/laser-diode-help-red-vs-blue-41970.html

oldscooliron · Jul 15, 2009

thank you

oldscooliron · Jul 16, 2009

Just to let everyone know after using a 3 ohm 1/2watt resistor on the DDL the peak ma is 475ma & set at 400ma lighting white matches now light instantly, white paper gets burn marks on both sides. I'll post a video soon!

DIY Homemade laser diode driver

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