Help with dual red setup.

[norty303]

am using Spaghetti and set the min and max output in the projector settings and the current was within limits. I set the upper limit at 300mA and the lower at 14mA

I keep reading this and canot make sense of it.
Are you saying you are using the software to limit the min and max current to the diode?

If so I would say this might be something eliminate from the chain first - unless you can be 100% certain that the max output can't be exceeded by the software.

What is the FM3 max output mA set to with 5V applied to mod?

[magman116]

I keep reading this and canot make sense of it.
Are you saying you are using the software to limit the min and max current to the diode?

If so I would say this might be something eliminate from the chain first - unless you can be 100% certain that the max output can't be exceeded by the software.

What is the FM3 max output mA set to with 5V applied to mod?

When I setup the flexmod, I set the max current at 840mA. I did have some issues with this FM3 after I first got it. It would not allow me to set the max current even though I could set the bias current. I put it aside for a couple of days and tried again and it worked that time. Could be a defective FM3 that is why I ordered 3 more.

[norty303]

So surely, having max current at 5V set to 840mA, you are asking for trouble if the software has any bugs or ways to output high power beams that bypass the max output.

At this point, I would think that if you actually set the output at 5V mod to 300mA on the FM3, you might stop blowing things up

[Solarfire]

So surely, having max current at 5V set to 840mA, you are asking for trouble if the software has any bugs or ways to output high power beams that bypass the max output.

At this point, I would think that if you actually set the output at 5V mod to 300mA on the FM3, you might stop blowing things up

He's running the diodes in parallel so 700-800mA could be ok.. But the FM3 max current has to be setup with 5VDC on the mod in of the FM3 to assure that the driver limiting is correct. If you’re still getting 600+mA per diode when modulating with a signal, then you’ve got a driver and/or resonance (if lasorb’s are used) problem.

[norty303]

Ah, ok, but I guess the sentiment is there - using software to limit max current is not a good approach, and introduces an unnecessary failure point. Better set the absolute max current required on FM3, then use software to reduce as necessary.

Of course, if the max current couldn't be set, this raises issues with the hardware.

I suppose the next question is:
Was the max current setup done as per the intructions, and what were the effects of not being able to set it? e.g. did the current just not increase/decrease when the pot was turned? What was its default value on switch on?

[mccarrot]

Maybe a thought:
A typical color modulation could be square wave, lets say 1Khz square wave.
Such square wave can have many harmonics resulting in high frequencies.

A diode also got a certain capacity, the higher the frequency the more current will flow trough a capacitor.

Maybe there is a difference between diodes causing one diode to get the full current when modulated at high frequencies.

But maybe it's better to not go this risky route just to save 25,- for a 2nd driver....

[magman116]

When the Fm3 was first powered up, as per the instructions, I was able to set the bias pot using no modulation. Then when I connected 5V to the modulation input, nothing happened. I believe the current was lower than when setting the bias. There was now adjustment when turning the pot. Then I tried it all over again with the same results. So I decided to put it to the side and work with another driver I had. A couple of days later I was putting together some more LOC modules and wanted to test the output and grabbed the FM3 again. This time I was able to adjust the bias and the max current. I set it at 400mA. Then I shorted the output and connect the LOC. It worked no problem. That is when I put it in the system and adjusted the current for 2 LOCs. Both LOCs powered up just fine.

Everything seemed to functional normally, but kept blowing the through Axis LOC. That is when I decided to start monitoring the current across the 1 ohm resistor.

Today, I added TECs to the LOCs and the driver heatsink. The driver heatsink was getting very hot. Too hot to touch for more than a second.

All 3 FM3s are mounted to a 4"x1-1/2"x1/4" aluminum jig plate.

After adding the TECs, it doesn't get very hot at all and the LOCs are cold to the touch. I ran the same frames that caused the current jump before and now there is no big current jump, there is an increase of about 50mA over its average range, but is staying within the max current setting of the FM3.

I think I will keep the TECs in to help with the heat. I am running them at 2A each. I still have not put TECs on the 445nm or the 532nm modules. I have about 20 40mmX40mmx4mm 50W TECs.

[dnar]

As your failures are always with the through-cube diode, I can't help but think you have something else wrong, like a faulty resistor, joint etc. When running parallel, any diode with dodgy wiring or resistoris going to damage the other diode(s).

[dnar]

Sorry for the double post. I setup a Flexmod P3 test today, using adjustable DC lab supply, function generator and a dummy load comprising 3 x IN4004 diodes + 1ohm resistor in series. Ignore the Mod signal going negative slightly, I used an AC generator and used a C/diode circuit to clamp/shift the signal.

The following DSO shots are measuring the following:
Trace 1 (Yellow): Modulation signal.
Trace 2 (Blue): LD current measured across the 1ohm resistor. 1mV = 1mW.

Setup procedure was as follows:
BIAS set with MOD at GND to 10mA
MOD @ 5V LD current set to 1000mA

PSU: 12V Freq: 2kHz Peak LD current: 1.02A

PSU: 12V Freq: 20kHz Peak LD current: 1.00A

PSU: 12V Freq: 200kHz Peak LD current: 0.776A

PSU: 12V Freq: 2kHz Mod: > 5V Peak LD current: 1.00A

PSU: 12V Freq: 20kHz Mod: >5V fast rise time Peak LD current: 0.968A

PSU: 12V Freq: 20kHz Mod: >5V Peak LD current: 1.00A

PSU: 24V Freq: 20kHz Mod: >5V Peak LD current: 0.992A

No signs of the LD current exceeding the configured setting! No signs of oscillation, ringing etc.

What is curious, is the phase shift between modulation and LD current at higher modulation frequencies.

Also, note the peak LD current when the PSU is raised to 24V. Not perfectly flat as with 12V supply.

I am hoping Dr Lava will add comment.

EDIT: And here is why I don't like running the P3 at 24V when driving a single LD or LD's in parallel:

PSU: 12V LD: 400mA

PSU: 24V LD:400mA

See how the current waveform is slewed in the rising edge?

[magman116]

dnar,

Great work!

I must say my waveforms do not look like yours at all. I will try to get some scope shots. Looks like you have a digital o-scope. Nice.

My waveforms look more like a PWM signal. It could be the DAC I am using and not the FM3s.

I am using the FSX2.0 DAC. http://www.ctrnd.com/NormLaserShow/FSX20.htm

dnar, what DAC do you use?