Testing DDL Circuit with multimeter

Hi again!
Ok i built both of the dummy load circuits, one with 4 1n4001 diodes and one with 4 green LED's.
I tested the 4 green LED's and found 4.16v, and with the bluray diode connected... i get the same thing! about 4.2v
When i test with the 4x1n4001 circuit, i get more than 5v (cant remember exact value)...
on both circuits i used a 100ohm 1/4watt resistor

The bluray diode emits a very weak dot, i was able to measure the current up to 40ma and didnt go above that.
one thing i noticed about the driver i have, it has 3 resistors on it... they are [brown, black, black, gold].
im showing that to be a 10ohm resistor = 30ohm.
is that why im losing so much voltage?

For a bluray diode it's best to use a 100 ohm resistor in parallel with the circuit instead of the silicon diodes. Did you use your 100 ohm resistor in the circuit after the LM317 or the way I just described? And what about the 3 10 ohm resistors, did you use those after the LM317 in parallel or series?????? :-?

this driver is a prebuilt i purchased a while ago. dont have the schematic of it, i suppose i could just look at the way it was soldered to find out. heres a pic http://i8.ebayimg.com/01/i/000/d9/78/2d41_1.JPG
I have everything i need to build another driver though.

For a bluray diode it's best to use a 100 ohm resistor in parallel with the circuit instead of the silicon diodes.
hmm... do you mean in the dummy load circuit?
The schematic here laserpointerforums.com/forumdata/yabbfiles/Attachments/prototype_001.jpg looks to be how this driver is setup, but in this pic theres (2) 20ohm resistors... on my driver, theres (3) 10ohm resistors.

when i build the new one, should i use a 100ohm resistor after the potentiometer?
Wouldnt that limit me to .0125 ma?
also, i dont know exactly how to refer to the resistors after the pot and the lm317... in DDL's schematic i see they are in series off the 'out' pin? if so, where would they be if they were in parallel.. before the 1n4001 across the positive and negative?
and just out of curiosity, what exactly does the 'adj' pin do in this configuration? i cant figure that out and i read through the spec sheet pretty well i thought.

On the schematic you posted, there's 2 10 ohm resistors in parallel making a total of 5 ohms resistance which let's through a maximum of 250mA, if the driver you have has 3 10 ohm resistors in parallel then it has a total resistance of 3.333 ohms. That let's through approx. 375mA.
Test your circuit again with the 100 ohm resistor in place of the silicon diodes.

oh i didnt realize that i should take the average of the resistors... i thought they added up. :

The way i tested it before... i had the 100ohm resistor and the (4) 1n4001's diodes in series across the LD nodes. i tested the MA by putting the multimeter leads on each side of the 100ohm resistor (so that would be right off the + after the capacitor, and off the - after the (4) 1n4001 diodes). I tested the voltage by placing the + lead of the multimeter inbetween the 100ohm resistor and the 1n4001 diodes, and the - right before it connected to the 1n4001 diodes.
exactly as seen here:laserpointerforums.com/forumdata/yabbfiles/Attachments/DDL_circuit_test01_001.jpg

I will connect just a 100ohm resistor tonight and test the V and Ma.

Thanks again Chido, sorry to bug ya so much... btw i bought a "building power supplies" book from radio shack, gonna read that on monday. Any suggestions on other reading material?

They add up when you connect them in series, like this ----[|||||]---- ----[|||||]----
When you connect them in parallel, like this  |----[|||||]----|  I'm not exacly sure
           |----[|||||]----|  
how to calculate that so I use this site. ;D

BTW, when using the 4 silicon diodes try to use a resistor with a smaller value, the reason why there's a 1 ohm resistor in the schematic is because you just have to set your DMM to mV and whatever you get will be your current, so 1mV = 1mA, if you use a 5 ohm resistor then you'll have to divide your millivoltage by 5, so in this case 5mV = 1mA, in your case it's 100mV = 1mA which is way to big and can be a little tricky to get accurate measurements.

Don't worry you don't bug me, if you did I would just simply ignore your posts. [smiley=evil.gif]
My suggestion is for you to read this entire thread, I read it when it was about 40 pages long and I had absolutely no knowledge of electronics, all I did was to google whatever I didn't understand, so if somebody mentioned resistors I goolged "resistor" to see what it was, when I read someone mentioned capacitors I googled "capcitor' to find out what it was. And so on with anything else I didn't know the meaning of until I finished reading the entire thread.

Hey guys,
This has been great review/confirmation for me as well. ;D
Chido,
You metioned that a voltage regulator could be added to the DDL circuit to achieve th required voltage to drive the current regulating circuit, would this be added in series before the DDL circuit? Would this be a "boost-circuit"?
I have become proficeient building "DDLs", but I would love to run my Blu-rays in a small 1x aa host. This would require a boost circuit for sure, but I am not sure how.

I said you could find some kind of regulator to boost voltage. You wouldn't have to connect it to a DDL circuit, you could just use it to boost the voltage and regulate the current of a certain battery to save space instead of using a 7.2v source to power the LM317 driver.
IgorT made a regulator that boosts voltage here, but I have no idea how it works since I haven't read about it so you should ask him. ;D

hey chido is it ok if i use 1/2 w 3 ohm resistor in my ddl driver to run my LG 20x dvd LD, do i need to secure the heatsink to run it well? i think i fail to secure the heatsink :-/ thats why i killed my red laser last time...

Dude, it is not ok for you to just barge in on threads asking questions, I just answered this question on the other thread, so please don't mess this one up.

ok sorry :-[...thanks. :-X

So would i be correct in thinking that for 420ma i would need 2.976 Ohms?

umm, yes :

Are you trying to spam, you posted the same question twice on the other page, I answered and now you ask again???? :-?

So sorry about that, had some sort of wierd connection problem ._. Didn't Notice it till now