Big problem with driver/test load

Hi guys, I have built some drivers for red laser diodes and a dummy load for testing...

first I build the driver from "Laser Driver - It Can Be Done" and the test load from the same site... all exactly like them... see the pics below..

but I have a problem I can't measure the current right... I used different batteries/power supplies and I can't seem to figure it out...

here is the deal ...

with my first dummy load accross the resistor I get 0.00mV whatever I do I can't get a reading (in fact my driver is set to 420mA and with laser diode it works just right)

so I thought my dummy load was bad - I build another the only differences are that my silicone diodes are 1N4007 instead of 1N4001 which can withstand more voltage (could that be the reason ... I don't think so)...

so I made another test. I have a Short Open Can Red Laser Diode which has burnt out and turned into a LED but it still works as current drainer so I hooked it after a 1Ohm resistor and tested the current there... I get a reading of 160mV ??? but my driver is set to 420mA or even higher but I can't get that reading there...

I tested my driver at 4.5V, 6V, 7.5V and the difference is somewhere about 40-50mV but still not the proper reading....

can someone explain to me is my driver actually supplying that amount of current or is there something wrong with my readings/dummy loads....

as a proof of my driver being ok I can tell that when I hook up a Long Open Can Red Laser Diode and driver being set to 431mA it is working just fine ... ???? so confused....... pls help:bowdown::beer::wtf::wtf:

Hmmm.
Instead of posting those schematics, which have been woking fine for everyone so far,
how about some pictures of your actual circuit?
Maybe you got a cold solder joint in your testload...

sorry I was at work...

here are the photos of my test load....

but also did you notice that I said when I hook up a burnt out diode with a 1 ohm resistor in series and measure the mV across the resistor I still get some inadequate readings...

I don't think there is a cold joint here I never make cold joints...:undecided::undecided::undecided:

p.s. just to say that I connect the output of the driver after the second diode for RED

Have you ruled out your multi meter? If you have a different DMM, or have access to one, give that a try.

Yep I just tested it with another DMM.... at 6V it reads 70mV at 7.5V it reads 145mV across the resistor ;((( when it should be 420mV

What IC are you using for your driver? It could be that the IC your using has a high voltage drop. Therefore you might need more voltage to get your calculated current.

Jufran88 said:

What IC are you using for your driver? It could be that the IC your using has a high voltage drop. Therefore you might need more voltage to get your calculated current.

Click to expand...

I have tried with L1117 and LM317 at different input voltages ... and I got only small difference at the output... I don't think it's a driver's issue.... I will try an expensive DMM today and post the results..

I suppose you can use the dead red diode as a test load, just to make sure the problem is not in the dummy.

Measure the input and ouput voltage and currents, perhaps that'll shed some light on the problem. 7.5 volts input voltage should be enough to drive a red within specifications for the LM317. For the L1117 it should be no issue at all.

problem solved

ok so I figured it out.... my 18650 battery can't supply the needed voltage and current .... although I thought it would ... when I use 2 x 18650 it sure does what it must (I measure 431mV across the resistor : FINALLY : :bowdown::bowdown

but excess voltage is too much and the l1117 gets too hot... I guess I need a 2 x 3V at best ...

damn I wanted a 1 battery operation :undecided:

anyways thanks for your help :: problem solved ::

I thought you said you tried 7.5V? As benm said that should have been enough. Its ok for the IC to get hot. With your set up it should handle the excess voltage/heat. If you think its getting too hot you could always heatsink it.

Yes I had tried it with 7.5V but my power supply seems to be some low current china power supply which couldn't deliver the right amount of current ... although it reads 1000mA MAX... that was my big deceive which mislead me of thinking something is wrong with my dummy load or driver... but after I tried some GOOD power supply it amazingly worked

Glad you got it figured out. Good luck with the rest of your build. :beer::beer:

Kevlar said:

Glad you got it figured out. Good luck with the rest of your build. :beer::beer:

Click to expand...

thanks kevlar :beer::beer:

p.s. TO THE MODERATORS: Feel free to close the thread :beer: