Newbie needs help!

[Ghostchrome]

Well, I'm not really too sure (electricity is still baffling to me), but the dummy load is simulating the draw that the laser diode would have, hence the drop in voltage.

You should be getting a reading in mV though accross the resistor in the dummy load.... :thinking:

 

[Ghostchrome]

Ah! That's it! Hook the DMM up across the resistor in the dummy load.

 

[hooshies]

Ah! That's it! Hook the DMM up across the resistor in the dummy load.

Getting a reading of 38 mV.

I'm not sure what this tells me about the driver itself. The reason behind setting up the driver was to have a regulated voltage output of 4.5V and 30mA.

I've been able to get the current to 30mA using different ohms in the driver, but I was under the impression that the DDL driver would also drop the voltage by at least 3V.

 

[Ghostchrome]

So 38 mV is good. 1mV=1mA across the resistor in the dummy load.

You mentioned above that you were shooting for 35 mA. Try hooking up a potentiometer and you should be able to pot it down more to where you want it.

 

[hooshies]

So 38 mV is good. 1mV=1mA across the resistor in the dummy load.

You mentioned above that you were shooting for 35 mA. Try hooking up a potentiometer and you should be able to pot it down more to where you want it.

I connected the pot and brought the current down to 30mA (which was what I wanted).

The issue for me is still the voltage, not the current. The laser module I have is rated for 4.5V. From the DDL schematics (Laser driver - It can be done) I thought that the driver would output 4.5V from a 9V source.

I guess I'm not understanding this correctly, but my ultimate goal is to have a driver that is outputting 4.5V and 30mA. When I connect a 9V battery to this driver, I'm getting a reading of 7.9V (without a dummy load) and 3V across the 4x1N4001 dummy load.

With a 5V wall charger, I am getting a reading of 4.7V (without a dummy load) and again the 3V across the 4x1N4001 dummy load.

The module I have now apparently has a driver, but I think the laser is burned anyways, as I messed up initially trying different things. But my problem still remains, that if I purchase another LD with (lets say) a 4.5V and 30mA rating, I know how to control the current with this driver, but how would I regulate the voltage at 4.5V?

 

[Ghostchrome]

Oh hrm... I'm not sure about that. Maybe someone else can chime in.

 

[LtKernelPanic]

This is one of those things that's hard to wrap your head around at first but once it clicks you'll go "Oh DUH! that makes sense now."

If your driver is set to output 30ma it will supply whatever voltage is needed to supply that current provided whatever you're powering the driver can supply it.

As an example I was testing a 635nm diode tonight with a simple LM317 driver set to 85ma powered by my bench supply set to 12v to simulate the 3x10440 LiIons that'll power the finished laser. Obviously the driver wasn't outputting 12v @85ma but more like 3-4v (or whatever the diode's need was) @ 85ma. All drivers will do the same. Your driver might take 4.5v in but only supply say 2.2v @ 30ma or whatever the needed voltage is to supply the preset current.

 

[Ghostchrome]

This is one of those things that's hard to wrap your head around at first but once it clicks you'll go "Oh DUH! that makes sense now."

If your driver is set to output 30ma it will supply whatever voltage is needed to supply that current provided whatever you're powering the driver can supply it.

As an example I was testing a 635nm diode tonight with a simple LM317 driver set to 85ma powered by my bench supply set to 12v to simulate the 3x10440 LiIons that'll power the finished laser. Obviously the driver wasn't outputting 12v @85ma but more like 3-4v (or whatever the diode's need was) @ 85ma. All drivers will do the same. Your driver might take 4.5v in but only supply say 2.2v @ 30ma or whatever the needed voltage is to supply the preset current.

Ah! Right on. Thanks for the clarification. :beer: