Adjusting Current With Multimeter?

[StuartB]

Just wondered if: With the current turned all the way down to start with and the voltage set somewhere between min and max of the diodes rating, is it ok to adjust the laser diode current using a multimeter in series with the diode, instead of using a string of diodes and resistor, or does it damage the laser diode?

Thanks.

 

[lasersbee]

Just wondered if: With the current turned all the way down to start with and the voltage set somewhere between min and max, is it ok to adjust the laser diode current using a multimeter in series with the diode, instead of using a string of diodes and resistor, or does it damage the laser diode?

Thanks.

You answered your own question.
You risk damaging or destroying your Laser Diode
while trying to set the current on a driver with
that small 1 turn pot.

Use a Dummy Load to be safe....

BtW.. It would be helpful if you added your
Global location to your Profile...


Jerry

 

[Encap]

You answered your own question.
You risk damaging or destroying your Laser Diode
while trying to set the current on a driver with
that small 1 turn pot.
Use a Dummy Load t5o be safe....
BtW.. It would be helpful if you added your
Global location to your Profile...


Jerry

exactly and do a Welcome post in the Welcome sub-forum if you expect any real help.

 

[StuartB]

You answered your own question.
You risk damaging or destroying your Laser Diode
while trying to set the current on a driver with
that small 1 turn pot.

Thanks for the reply.
It's actually a multiturn pot (the blue one with the gold screw) not a 1 turn, so it would only increase the current very gradually.
I don't see how it could hurt the laser diode but was'nt sure. I asked because I've never seen anyone using the multimeter method.

To me it seems to be an obvious way of doing it, you would get a more accurate reading as you are measuring the actual current through the laser
and not just through a bunch of diodes and a resistor, which would all have manufacturing differences/tollerances.

 

[hakzaw1]

don't do it.... 'Dummy' load.. not sure if the load is the dummy or its the one loading

..JK lol --

easy to build. Lbee for many years sent out the parts free.. but now you need higher power.

 

[paul1598419]

The only safe way to set the driver is with a dummy load. All these pots have inherent noise caused when adjusting them. The dummy load is a very good approximation of the laser diode's load, and after all, we are setting the maximum current the driver will allow the diode to pull. For that reason, the dummy load is very close to what the driver "sees" when the Vf changes with temperature.

 

[hakzaw1]

yeah WHAT ^^^ HE SAID

 

[StuartB]

Ok.
Thanks very much, you've convinced me. If I had a spare one I could sacrifice I might give it a go, but I only have the one.

 

[diachi]

Everyone has answered already, dummy load is the only truly safe way to do it.

It's not just the chance of slipping and turning the pot too far, or something like that. Turning the pot can also introduce noise into the output as the wiper moves along the resistor strip inside of the pot. (As Paul mentioned)

Making a dummy load is fairly straight forward, there's lots of information on here and on the internet in general about constructing one. Components are readily available, even for large test loads (I put together a 20A test load earlier this year!). They behave just like a laser diode electrically and as such are perfect for testing drivers. You can even use an ammeter in series with the dummy load if you want to rule out any error introduced by a current sense resistor.

Good luck. :beer:

 

[hakzaw1]

+rep for Diachi
this thread is done

 

[lasersbee]

Thanks for the reply.
It's actually a multiturn pot (the blue one with the gold screw) not a 1 turn, so it would only increase the current very gradually.
I don't see how it could hurt the laser diode but was'nt sure. I asked because I've never seen anyone using the multimeter method.

To me it seems to be an obvious way of doing it, you would get a more accurate reading as you are measuring the actual current through the laser
and not just through a bunch of diodes and a resistor, which would all have manufacturing differences/tollerances.

My mistake... It is a 10turn pot.
Without putting the Driver output on a
Scope you will not know if the output spikes
under adjustment.
Using a Dummy Test Load increases your chances
to not damage/destroy your LD.

The ultimate choice is yours...

Jerry

 

[piya19]

hello,
im new into this forum im using the same current driver to drive my osram PLTB450b blue laser diode, since im not good with the electronics part much i needed help,in the above current driver i could see my voltage value using a multimeter, but i couldn't see any current value even after turning the screw so my doubt is, is it potentiometer pot used to calculate the resistance and then should i calculate the current with the set voltage?

 

[Lifetime17]

Hi,
You need a test load no direct voltage to the diode DOA!! Get a test load from Survival Lasers . They sell them you want a 3A test load.

Rich

 

[jors]

or measure current on the dc input. Reading is almost the same.

 

[paul1598419]

or measure current on the dc input. Reading is almost the same.

That really depends on the driver as they dissipate power as heat. Linear drivers can be especially prone to this. The only accurate way is to measure the current after the driver...or at the dummy load.

 

[jors]

That really depends on the driver as they dissipate power as heat. Linear drivers can be especially prone to this. The only accurate way is to measure the current after the driver...or at the dummy load.

Yep, right. However dummy load is not exactly the same load than a Laser diode. So this is not 100% accurate, but yes, maybe the better approach. There are some drivers with current balance resistor on the output. On this drivers, Another way is to measure voltage falling across this resistor, and calculate indirectly current flowing thru LD by Ohm law. But resistors have some tolerance, and it also changes a bit once get hot. So this is not 100% accurate as well.
I've tested several drivers with Dummy load, and compared current reading on the Dummy vs. current drain on the DC input (2 multimeters). I've noticed difference is only -0,2A in the DC input in most cases.
So now, I adjust just reading current on the DC input with LD in place. I only have to 'add' +0,2A on the target current. This is the most practical way in my opinion, but you have to measure your driver 1st with Dummy like I did to know its current 'linearity' offset.
Above works ok for me with drivers for laser show that have input modulation. Could this also work for your laserpointer-type small drivers?