HELP! dvd diode not workin but drawing current

[Thories]

hi there i just got 2 diodes out of a dvd reader /writer and i found one to b infrared (used mobile phone to see it ) and the other one which i assumed to be red wont work... ive got the polarity right i know cos i tested on multimeter however i hook it up with bats and resistor and no light..... its drawing current... so im unsure to what the problem could be HELP!!! if its drawing current does that mean its ok? i hope its not dead...

 

[SenKat]

How much current, and how much voltage are you putting into it ? I believe the minimum lasing threshold to be around 2.4 volts.

 

[Thories]

i first used 2, 1.5 V 120 ohm resistor.... then i used 3, 1.5 v with a 180 ohm resistor.....

 

[SenKat]

Try using just the two 1.2v without the resistor...a SHORT test !

 

[Thories]

Uh do u mean the two 1.5 v?? also do they need to be in the black housing to lase red or something??? cos i could see infra red being emitted by using my camera in my phone.......atm they are just two tiny little circles on some board

 

[SenKat]

You should be able to get it to power up pretty well with just using the two 1.2v batts - you can try with the alkies, but that's up to you ! Just do NOT use lithium batteries in it !

 

[Thories]

sorry to be a little slow but the batteries i have are 1.5v not 1.2.....

 

[SenKat]

If you have alkalines, they are 1.5v - if they are NiMh - they are most likely 1.2v...either way, forget the resistor for the test....Just hook em up, and see if it lases !

 

[Thories]

ok i aimed it at my carpet reasonably close... and all i could see was a dull red glow.... and from the other one i saw nothing on carpet but the mobile saw heaps of what i assume to be IR

 

[Thories]

actually cancel that i used no resistor and BOOM bright red laser all over my floor... just hadent have got the ends tinned properly with solder... but how should i run it normally... i cant run it without a resistor for long can i? cos it will kill the diode right? any suggestions?

 

[Hemlock_Mike]

WOW -- You took the BIG step SenKat & I only talk about !!
NOW--- HEAT SINK and back down a little with a 1.0 to 2.7 ohm resistor and a capacitor across the LD. Glad you didn't toast it -- you just needed a little more drive !!

Mike

 

[Thories]

thats pretty low resistance lol ive been using 120 - 180 ohm resistors with my 2 AA's..... what size capacitor would you recommend? ... my friends think im totally nuts messing with these lasers

 

[Hemlock_Mike]

Thories --

YES --- you are crazy. PERIOD......

You need to monitor the LD current. PERIOD .......
Do the math -- 3 volts across a 120 ohm resistor gives only 25 mA.  This does not even account for the Vd across the diode junction.  The LD won't even start to lase untill it's up to about 70 mA.  I use an LM317 current source to do my testing.

Look up posts on red laser projects from several months ago.  My DVD diode ran at 200 mA with 2.48 volts across the LD.  That gave me 110 mW output.
This is a "safe" start -- ymmv................

At 2.55 volts across the diode, you "may" read 300 mA and have 170 mW output.  It all depends on your specific LD so it's important to meter everything as you turn up the watts !!
Learn as you go - I learned by toasting a few diodes :-(     Make sure the diode has good heat sinking. Capacitor 10 to 100 Mfd.

Mike

 

[Thories]

ill slowly bring down the resistance ( ive got a huge box of resistors in small steps that will be very handy ) hopefully tonight i might mount it.... um what should i be doing about lenses. how focused will this thing be? will the optics from the dvd drive be useful?

 

[Hemlock_Mike]

A resistor decade box might make too big a step at the low end. The diode junction v/I curve is not linear. Remember that SenKat and I have done a lot of testing and paid the price !!! Failure is just a learning experience.

Decade boxes can make severe steps - that's why a 100 Mfd cap is so important because it can soak up some surge current damaging to the LD.

There's lots of info on this forum and CPF about doing this. READ READ READ.
Aixiz (or something like this) has modules for about $12 which work well for heat sink and adjustable focus. That is also on these forums.

Mike

 

[Thories]

hmmm thanks ill see if i can salvage that capacitor tonight.... for the resistors i dont have anything below 10 ohms... so when if i need it i can make some in parallel and test till i get the right resistance. ill be sure to monitor the current... ill keep it below 200mA i don't wanna be greedy until i have a better job . i most certainly will continue reading as much as i can on these forums. as for the heat sinking and lens stuff i might try making my own, i have all the stuff i should need from the dvd (lenses) and ive got some old heat sinking compound and thin copper stuff in a box somewhere. while im testing is it ok that it goes without heat sinking and maybe only have it on for VERY short durations like a few seconds? anyway hopefully ill be able to put this into my stylish bright orange case....SenKat suggested just banging in a 1 ohm resistor however i might be a little more cautious as this is my only laser diode atm (*50 mW* ebaser coming Tuesday)