LD driver configuring questions

[catalanjo]

WILL YOUR MULTI-METER MEASURE AMPS

It's AMPS or static (very high volts) that tend to kill diodes !

Always,always,always .. use a current meter (or driver card "current monitor" test points if only voltmeter available) when first trying out a diode.

I edited my earlier post ...might be worth re-reading.

Cheers

Sorry about dead diode ....this is always sad !

[planters]

When you are setting up the driver circuit you can confirm that everything is in order by temporally installing a simple resistor across the driver output in place of the laser.

All these diode lasers have spec sheets that give a nominal voltage drop and recommended current. Size a resistor that will produce approximately this voltage drop at the current you plan to operate at. Now, you can insert a multi-meter in series and then in parallel to confirm that the driver is doing what you want under operating conditions. You can also place an oscilloscope in parallel with this resistor and examine the instantaneous voltage across this resistor when modulating the driver. This can identify any transient voltage spikes and voltage sag.

[Maltes]

I'm not sure if my diode has really died. I could check if the same setup I have works with another diode but I'm hesitant to get another one killed.

If this migth be helpful, if measuring the voltage that goes from the driver to the diode, it shows 0 but at some point when I slowly rotate the Gain pot it jumps to 12.5, the voltage from the PSU. This is when the diode is connected. Anyone have an explanation for this?

[planters]

Did you read my post #42?

[VDX]

... I'm testing and adjusting my drivers with a 0,1 Ohm - 5W-resistor (read my post #5).

It's not the same voltage-drop, as with the diode, but as the drivers are constant-current types, they only need a "ballast" to regulate the load ...

Viktor

[catalanjo]

Sorry but I am getting a bit lost here!

@ "if measuring the voltage that goes from the driver to the diode" .... this is not clear to me at least !

To measure a voltage (difference) you put the test probes to two different points ....which two points are you referring to here specifically ?

Voltages don't really GO anywhere...they are present or not present ...please explain further.

Cheers
It really does make much more sense to measure current ...either by inserting a known series resistor and measuring the voltage across it, as Planters suggests, or by connecting the multimeter in high amp range directly in series.

[Maltes]

Sorry I did not respond to your suggestion on measuring the current the first (few ) time. I'll do that and let you know.

I mean the voltage on the diode + and diode - pins of the driver, or the cathode and anode of the diode.

EDIT: Okay tested
Amps: 0 amps to the diode no matter the Gain pot value, 7.7 mA from PSU to driver
Volts: at some exact spot on the Gain pot, the voltage on the diode pins jumps from something like 0.14V to 12.5V (same as from PSU).

[catalanjo]

Very odd readings,...... it seems LD has gone totally open circuit,....... never seen that before at low currents, .... have to cogitate a bit.

Zero amps thru diode means.....R.I.P. ..sorry !

Don't spose you have a scope, ( as Planters suggests) to see if there is a load of noise from somewhere ...... what make is PSU ?

What happens with just amp meter and a fat high wattage resistor connected across driver output when gain pot (primary suspect) is moved about ?

Cheers

[planters]

Maltes,

I am going to insist that you INSERT A RESISTOR and measure the current flow through this resistor and the voltage drop across it!

If you are doing this then I agree with catalanjo that these are odd readings. But, if you are measuring the voltage across the open driver then the poor driver is trying to drive your multi meter and will never be able to pass any meaningful current through it up to the PSU supplied limit.

Almost always, when a laser diode breaks, it will continue to draw current, it just doesn't produce any light.

[Maltes]

Don't spose you have a scope, ( as Planters suggests) to see if there is a load of noise from somewhere

I don't.

...... what make is PSU ?

Its a generic 160W 12V PSU.
I'm probably going to get a new one anyway since it is not powerful enough for my final build and is making the noise they make when they are getting close to dying.

What happens with just amp meter and a fat high wattage resistor connected across driver output when gain pot (primary suspect) is moved about ?

I will try this. I know planters suggested this before. I just not sure how to calc what resistor I need to get.

If you are doing this then I agree with catalanjo that these are odd readings. But, if you are measuring the voltage across the open driver then the poor driver is trying to drive your multi meter and will never be able to pass any meaningful current through it up to the PSU supplied limit.

There wasnt a resistor used, but the diode was there.
The meter was connected in series with the diode, driver+ -> multimeter probe -> diode+, diode- -> multimeter probe -> driver-

Almost always, when a laser diode breaks, it will continue to draw current, it just doesn't produce any light.

Then this is very odd indeed.