Diode Current Measurement

[kurtwx]

So I have 3 or 4 blu lasers up and running and the same number in the garbage can looking like dim blue LED's. I haven't used the 1 ohm resistor method of measuring current to the diode and generally check current at the battery. Knowing the drain on the battery is different than the current draw on the diode anybody know how they correlate? I just bought a dummy load so I can better adjust my diodes. I am using home built LM317 type drivers.

KW

 

[rog8811]

If you have 2 1ohm resistors you can answer that for us, one in the test load, one in the line from the battery. Measure, compare, post the result.
My guess :-/ around 2mv......
Regards rog8811

 

[laserfreak3d]

just connect a multimeter in amp mode to the driver and measure it.
And tune it while measuring

havent had one die on me yet because of over current
u can use a dummy load but u dont realy need one.

 

[rog8811]

just connect a multimeter in amp mode to the driver and measure it.
And tune it while measuring  

Connect it how? tune it how?

havent had one die on me yet because of over current
u can use a dummy load but u dont realy need one.

Not the kind of advice I would give this poster having read his post

Let us have a look at the ONE and ONLY post from this new member shall we?

So I have 3 or 4 blu lasers up and running and the same number in the garbage can looking like dim blue LED's.

So he is trying but having problems.

I haven't used the 1 ohm resistor method of measuring current to the diode and generally check current at the battery

Not too much of a problem there...only thing is as the driver has not been tested with a dummy load there is just the chance something is wrong.

I just bought a dummy load so I can better adjust my diodes. I am using home built LM317 type drivers.

Good man, use it whenever you build a new driver, it will save heartache and money on more LD's, just remember to short out the capacitor before connecting up the LD

Out of interest what sort of power are you aiming at? I have found that 110ma is a safe(ish) current. I was serious about measuring input and output current, I do not recal the figures being posted before.

Regards rpg8811

 

[kurtwx]

sO BACK TO THE POINT OF MY ORIGINAL QUESTION. What is the difference in current draw between the battery and the circut and the circut and the diode. The LM317 I'm sure wastes some power just like any regulator. I have been measuring my ma draw in series with the battery and I know this is probably giving me a false high reading. I will take the first suggestion and put a one ohm resistor in series with both the battery and the diode and do the voltage drop test.

Thanks

KW

 

[lasersbee]

You can't get better advice than what Rog8011 posted...

Jerry

 

[lasersbee]

sO BACK TO THE POINT OF MY ORIGINAL QUESTION. What is the difference in current draw between the battery and the circut and the circut and the diode. The LM317 I'm sure wastes some power just like any regulator. I have been measuring my ma draw in series with the battery and I know this is probably giving me a false high reading. I will take the first suggestion and put a one ohm resistor in series with both the battery and the diode and do the voltage drop test.

Thanks

KW

Read what rog8811 wrote in his 1st reply..... :-?
(I believe he meant... 2mA of current... read as 2mV across the 1 Ohm resistors.. )


Jerry

 

[kurtwx]

SO AN ANSWER TO MY OWN QUESTION. i HOOKED MY DIODE UP TO MY lm 317 DRIVER AND HOOKED UP MY METER IN SERIES WITH THE 9V BATTERY. i ADJUSTED THE CURRENT UNTIL IT WAS DRAWING 120MA FROM THE BATTERY. I THEN PUT THE METER IN SERIES WITH THE DIODE AND FIRED IT UP. CURRENT TO THE DIODE WAS 82MA AND I ADJUSTED IT UP TO ABOUT 110MA. i THEN PUT THE METER BACK IN SERIES WITH THE BATTERY AND I WAS SURPRISED TO SW PRETTY MUCH THE ORIGINAL 120MA. THIS DOESN'T MAKE PERFECT SENSE BUT I THINK IT HAS TO DO WITH HOW THE LM317 WORKS. THE DRIVER I AM WORKING WITH IS ABOUT AS SIMPLE AS THEY GET. LM317 REGULATOR 47UF CAP AND A 50 OHM 25 TURN POT RUNNING ON A 9 VOLT BATTERY. I GUESS THE IMPORTANT THING FOR NEW GUYS IS TO MEASURE THE CURRENT BETWEEN THE DRIVER AND THE DIODE NOT THE DRIVER AND THE BATTERY. DANGEROUS TO DICONNECTING DIODE TO MEASURE SO USE THE 1 OHM RESISTOR METHOD DESCRIBED ABOVE.

kw

 

[lasersbee]

SO AN ANSWER TO MY OWN QUESTION. i HOOKED MY DIODE UP TO MY lm 317 DRIVER AND HOOKED UP MY METER IN SERIES WITH THE 9V BATTERY. i ADJUSTED THE CURRENT UNTIL IT WAS DRAWING 120MA FROM THE BATTERY. I THEN PUT THE METER IN SERIES WITH THE DIODE AND FIRED IT UP. CURRENT TO THE DIODE WAS 82MA AND I ADJUSTED IT UP TO ABOUT 110MA. i THEN PUT THE METER BACK IN SERIES WITH THE BATTERY AND I WAS SURPRISED TO SW PRETTY MUCH THE ORIGINAL 120MA. THIS DOESN'T MAKE PERFECT SENSE BUT I THINK IT HAS TO DO WITH HOW THE LM317 WORKS. THE DRIVER I AM WORKING WITH IS ABOUT AS SIMPLE AS THEY GET. LM317 REGULATOR 47UF CAP AND A 50 OHM 25 TURN POT RUNNING ON A 9 VOLT BATTERY. I GUESS THE IMPORTANT THING FOR NEW GUYS IS TO MEASURE THE CURRENT BETWEEN THE DRIVER AND THE DIODE NOT THE DRIVER AND THE BATTERY. DANGEROUS TO DICONNECTING DIODE TO MEASURE SO USE THE 1 OHM RESISTOR METHOD DESCRIBED ABOVE.

kw

It is bad etiquette to write in ALL CAPITALS

it is called SCREAMING

Besides it is so hard to read that way..... that I'm not even going to try..:-/

Jerry

 

[kurtwx]

We'll don't read it then. One of those speed typing things when you get half way through and realize the caps were on and lack the ambition to type it over again.

KW

 

[rog8811]

Interesting figures 120 / 82, then 120 / 110, I cannot pretend to understand that unless the DVM is not telling the truth, you must put a 1 0hm in both places and measure...(I would do it myself but it is too cold in the workshop at the moment )... it would finally answer the question as at the moment you are not doing like for like by measuring mv in one case and ma in the other.

Regards rog8811
[edit]If you trype in caps again, in error, just put an appology at the bottom for the mistake, it will prevent you from being jumped on as it is considered bad etiquette [/edit]

Another edit, I have just seen this in another thread and Gazoo makes a good point that I had not considered, you have not stated what you are using for your supply, if 9v PP3 battery read on.
[edit]

If you are referring to the transistor radio type 9 volt, it wouldn't be a good idea because they have a max discharge rating of 120ma's. Anything above that and the battery will probably shut down

Gazoo, you have done it again   I am going to post this on another thread as I had not considered that as a limiting factor on some measurement being taken.

Regards rog8811[/edit]

 

[kurtwx]

Yes I was using a standard 9 volt battery. Thanks for the info on the current limitations of this battery. Once I get the right battery and the 1 ohm resistors installed I'll repeat the test. I live in a small town and one ohm resistors are a little hard to come by. I'll have to wait for the next trip to the big city.

KW

 

[LarryDFW]

kurtwx;

Since the #317 regulator is not a switching type...

the current you read from the battery, should also be the current thru the LD.

LarryDFW

 

[rog8811]

the current you read from the battery, should also be the current thru the LD.

That is what i would have expected, hopefully kurtwx will be able to confirm it when he has it all set up.

Regards rog8811

 

[kurtwx]

OK so I just did the test again with a proper 12v powere source. I tested the circut with my meter in series with the batteries and then in series with the diode. LarryDFW is correct the current draw on the battery was the same going to the diode - in this case about 110ma. I had always assuned that the LM317 consumed some power so the draw on the battery would be more than the ma going to the diode.

Thanks for the helpful comments.

KW