FlexMod P3 Analog/TTL Laser Diode Driver

[kingjamez]

Hi Guys,
I just burned out 2 brand new diodes with my FlexMod P3 and would appreciate it if you could help me diagnose why I'm killing diodes:

Edit: It wasn't the Flexmods fault!

Thanks for the help.

-Jim

[The_Doctor]

How are the diodes fitted to the copper clamp? If Briggs (Dan) is willing, it may be possible to have a close look at the die to see if it was loosened by a deformity caused by a clamping action.

As far as I can tell from a bit of quick reading on two related P3 threads, that LED will light up only if an interlock is broken, or a diode connection fails causing a sharp drop in current that the driver did not intend. Normal facet damage caused by ESD or overcurrent or retroreflection will not cause the diode current draw to change unless the power, and not the current, was being controlled. This means that you may have a mechanical failure in the diode mounts. As you say that both failed diodes came mounted the same way, this is worth looking into.

[swamidog]

don't use bullet connectors. solder directly.

Hi Guys,
I just burned out 2 brand new diodes with my FlexMod P3 and would appreciate it if you could help me diagnose why I'm killing diodes:

The first is a S06J diode purchased pre-installed in a copper module. I hooked it up to the Flexmod P3 that was connected to a regulated 9.0 vdc power supply. The Flexmod P3 was tuned with a fluke multimeter for 35ma bias current and 165ma full current for initial testing. The S06J diode was connected to the Flexmod P3 with 2mm bullet connectors.
The first time I used the diode I turned on the power and the diode started to lase at the bias voltage. I then connected the modulation lead of the Flexmod to 5v to set the current draw to 165ma. The diode responded and brightened as expected, for about 2 seconds, then dramatically reduced in brightness. It never recovered. It's now a 405nm led.

Thinking I just had bad luck, I then ordered an Osram PLTB450B again pre-installed in a copper module. It arrived yesterday and I used the same setup to test it. The only difference was that I set the full current to 1.00 amp with the fluke multimeter. Again, the diode lased at 35ma bias current, but this time when I applied the 5v modulation input for full current, the Flexmod went red and the output to the diode stopped. I disconnected the interlock, and reset the Flexmod to low current. I then reconnected the interlock and the diode lased again at 35ma bias current. I again applied 5v for full current, and the Flexmod went red again. However, now after resetting it, the Flexmod will not light the diode at all even at bias current. It is completely dead, no output at all and the Flexmod always stays red when it is attached.

Now, I would suspect the Flexmod is killing the diodes. However, I have it running other 405nm and 445nm diodes with no problems. In fact it's powering an old A140 diode at 1 amp right now and working like a champ (exactly the same setup that just killed the Osram).

Any ideas?

-Jim

[kingjamez]

How are the diodes fitted to the copper clamp? If Briggs (Dan) is willing, it may be possible to have a close look at the die to see if it was loosened by a deformity caused by a clamping action.

As far as I can tell from a bit of quick reading on two related P3 threads, that LED will light up only if an interlock is broken, or a diode connection fails.

Thanks for the help!

The diodes came preinstalled in a copper "Aixiz" style module, I'm guessing they are press fit in with a jig for safety and consistencies sake.

I'm in total agreement on the Osram diode. It appears that it is now "open" (this is confirmed with my multimeter). I haven't seen a diode fail that way before. Everytime I've killed one in the past they still draw current, the Osram does not.

The S06J does draw current, it's just DEAD... Which is disappointing after having applied only 165ma.

-Jim

[kingjamez]

don't use bullet connectors. solder directly.

Can you help me understand why the bullet connectors could cause these failures? The connectors are very tight, and I've used these connectors for years with other laser projects. They have a very very low internal resistance, they are rated at up to 20 amps. I didn't disconnect them at any point during the testing of these brand new diodes.

-Jim

[dkumpula]

I just received some of the new Flexmod P3s with the beam suppression option and had my first go with them this morning. I have installed several of the standard Flexmods in the past, so I thought it might be useful to capture a couple notes regarding the modifications required for these beam suppression units and their behavior.

1. First, the new instructions included for modifying the P3s by soldering two additional resistors were clear and accurate - at least for me. They arrived with the package from Andrew as black and white copies, but you can find the original with color pics if you'd like here: http://innolasers.com/laser/FlexModP...dP3_Manual.pdf
   
   
2. The only thing I questioned when I was looking at the minor modifications was the solder point described here as: "solder the 47k Ohm resistor from the top end of the small black component to the leftmost via hole visible of the set of 3 on the bottom right". You really do solder it onto the top lead of the black component more or less as described, but I looked carefully at the photo in the instructions to ensure I was attaching it at the correct place.
   
   
3. The order of the resistors in the instructions is somewhat important as it would be a bit difficult to solder them in the reverse order as everything is tiny and close together on the Flexmods. A steady hand and a sharp point on your soldering iron is essential. A magnifying glass is also useful.
   
   
4. An active ILDA signal (for whatever color your Flexmod is being modulated by), is required to turn off beam suppression, of course, but note that the red LED comes on when beam suppression is active. This LED isn't an indication of a broken interlock or disconnected diode as it is on the standard P3s as those features are disabled when you enable beam suppression. As I powered up without an active ILDA signal for that particular driver, the red LED threw me off for a minute, but it makes sense after I thought about it.
   
   
5. Since you need an active modulation signal to turn off the beam suppression, I set the bias potentiometer with the gain turned all the way down. After getting bias set properly, I adjusted gain to the desired level. There might be alternative approaches here as well.
   
   
6. In addition to the interlock and open output loop sensing functions not being available as described in the instructions when you have enabled the beam suppression option, the start-up delay appears to also be turned off.
   
   
7. One final note: My package from Andrew included a capacitor whose purpose wasn't described in the instructions. I am told that it is used to compensate for inductance when there are long leads to between the Flexmod and your diodes. In my case, I keep the Flexmods close to the diodes with leads that are only a few inches long, so I haven't used the capacitors myself.

That's all I have noticed in regards to the beam suppression model thus far. I would encourage any other notes and/or corrections that you may notice as you install and operate these devices.

-David

[Galvonaut]

Very informative post David. Thank you. I will find that handy when I eventually get round to ordering my FlexMods!

[kingjamez]

David: What type and value capacitor is now included to help compensate for long lead lengths?
-Jim

[dkumpula]

David: What type and value capacitor is now included to help compensate for long lead lengths?
-Jim

They are 270 uF. It would be nice to have some guidelines for when they should be used. I keep my flexmods close to my diodes, but is 4-6 inches of leads enough to start using them? I don't know. Maybe an engineer can chime in here.

David

[buffo]

Hold it guys...

That capacitor is supposed to go on the POWER INPUT side of the flexmod. It does not go across the diode!

It's designed to smooth out any voltage drop if your power supply can't keep up with the load.

Andrew explained it at the NWLEM. He was thinking about the funny spikes I observed on my flexmods when running them at high currents. He theorized that part of the problem may have been a momentary dip in the supply voltage. That would explain the spikes, both positive and negative. I just got a new oscilloscope, so I hope to replicate my tests this weekend to see if the capacitor helps.

But just to reiterate: that cap does not go across the output of the Flexmod! It's designed to be installed on the power input side only. And it has nothing to do with the lead lengths from the flexmod to the diode at all.

Adam