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Driver test

alessnilsen

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Hi there! I bought this driver to drive a NUBM08 diode, but before I connect it to the driver, I would like to test it, but I don't know what to look at.

My idea is to connect three diodes in series with a ampmeter to make a test load and conect a osciloscope in paralel with the driver output. With that setup, I set the driver to 4,7A, higher that I need, I suplied the TTL with 3,3V 1,6Khz signal and tested at various PWM settings, this is what I got:

scope_0.pngscope_1.pngscope_2.pngscope_3.pngscope_4.pngscope_5.png

I see a very high peak when the driver switch the current ON, also the pulse is not clean. The forward voltage is set to 3,5V. My knowledge says that this peak can kill my laser diode, my question is, is this driver defective? Should I use it?

The driver in question is this one.

Thank you!
 



diachi

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Feb 22, 2008
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Hi there! I bought this driver to drive a NUBM08 diode, but before I connect it to the driver, I would like to test it, but I don't know what to look at.

My idea is to connect three diodes in series with a ampmeter to make a test load and conect a osciloscope in paralel with the driver output. With that setup, I set the driver to 4,7A, higher that I need, I suplied the TTL with 3,3V 1,6Khz signal and tested at various PWM settings, this is what I got:

View attachment 65620View attachment 65621View attachment 65622View attachment 65623View attachment 65624View attachment 65625

I see a very high peak when the driver switch the current ON, also the pulse is not clean. The forward voltage is set to 3,5V. My knowledge says that this peak can kill my laser diode, my question is, is this driver defective? Should I use it?

The driver in question is this one.

Thank you!

5-6 diodes would probably be a better comparison for a test load. You want the voltage drop across the diodes to match the voltage drop across the diode as closely as possible (4.5-4.6V for the NUBM08 at those currents). Look at the datasheet for your diodes and see, the voltage drop will vary with current and temperature.

For measuring current best practice is to put a shunt resistor in series with the diodes and measure the voltage drop across that. Then measure the voltage drop across the diodes if you want to know that.

Oscilloscope right on the driver output to view the output signal.

Have you verified your input signal is good? A garbage signal in will give you a garbage signal out.
 

alessnilsen

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May 20, 2013
Messages
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Need to check this out, the first test I did was with 8 diodes, then I started to ditch one by one, until the output voltage reached 4,5V, I could have messed this up, because I was using a 1Ohm resistor, so at 4,7A it would have 4,7V across it.

I grabbed a 0,68Ohms resistor and tried again with 6 diodes, since I didn't have 6A+ diodes, I had to put the dummy load under water to keep it cool. To generate the PWM, I used a Arduino Mega doing a sweep from 0 to 100% at frequencies of 490Hz and 980Hz.

At first it looked OK, same result, but as I was increasing the current I started to hear a buzzing noise comming from my power supply and the driver, the buzz matched the PWM modulation, I trough my 10A PSU wasn't enough for the high current pulses, so I added a massive 16000uF/50V capacitor in parallel with my PSU, it stopped buzzing but the driver not.

As I was adjusting the current, there was a time that the driver just stopped regulating the voltage, showing huge spikes at the output. I turned it off, disconected the PWM signal and turned it on again to have a steady reading of the output current, short time after I turned it on, smoke started to come out of the driver and it stopped working.

I already contacted the seller to see if I could get a replacement. I will update this when possible.

20190724_234847.jpg20190724_234830.jpg

This is the result of the same setup on another driver (this one is limited to 2,4A).
20190725_002954.jpg20190725_003006.jpg20190725_003016.jpg
 
Last edited:

diachi

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Feb 22, 2008
Messages
9,793
Points
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Need to check this out, the first test I did was with 8 diodes, then I started to ditch one by one, until the output voltage reached 4,5V, I could have messed this up, because I was using a 1Ohm resistor, so at 4,7A it would have 4,7V across it.

Better going down to 0.1Ω when you get up to those currents. Using my 20A test load as an example, a 6 diode setting would produce a drop of somewhere around 4.2V across the diodes. Add the 4.7V across your 1Ω shunt and your driver now needs to output 8.9V. A 0.1Ω shunt drops that down to 4.67V. My test load uses 8x 20A (4 sets of two for 4 different adjustable ranges) rectifier diodes and 100W 0.1Ω shunt, will sit and do 20A all day with the cooling fan on set to full voltage drop.

I grabbed a 0,68Ohms resistor and tried again with 6 diodes, since I didn't have 6A+ diodes, I had to put the dummy load under water to keep it cool. To generate the PWM, I used a Arduino Mega doing a sweep from 0 to 100% at frequencies of 490Hz and 980Hz.

Easiest to stick to 0.1/1Ω shunts, means you can read the current without doing the math. Doesn't hurt to keep them around in varying wattages. I have 1/4W, 1/2W, 5W, 10W and 100W.

Grab some 20A TO-220 rectifier diodes. They're not expensive and can easily be mounted to a heatsink (with fan if you need100% duty). Submerging them in water isn't the best idea, especially if you're not using DI water. Pure DI water isn't very conductive, but if you have any sort of solutes present in the water then it will become conductive. Will do funky things, especially with any sort of pulsed output.


At first it looked OK, same result, but as I was increasing the current I started to hear a buzzing noise comming from my power supply and the driver, the buzz matched the PWM modulation, I trough my 10A PSU wasn't enough for the high current pulses, so I added a massive 16000uF/50V capacitor in parallel with my PSU, it stopped buzzing but the driver not.

Your 10A PSU should handle the load from a switching current regulator at 4.7A just fine, those switching drivers are quite efficient. Wouldn't expect more than 6A load on your PSU if the driver is bucking (Vin>Vout). What was your input voltage?

As I was adjusting the current, there was a time that the driver just stopped regulating the voltage, showing huge spikes at the output. I turned it off, disconected the PWM signal and turned it on again to have a steady reading of the output current, short time after I turned it on, smoke started to come out of the driver and it stopped working.

What driver are you using?

I already contacted the seller to see if I could get a replacement. I will update this when possible.

View attachment 65636View attachment 65637

This is the result of the same setup on another driver (this one is limited to 2,4A).
View attachment 65638View attachment 65639View attachment 65640

A proper test load goes a long way.

Again, what does your input signal look like? The spikes on your original post are <3V peak to peak (which won't damage that LD), as though the driver input isn't getting driven fully by the signal source. PWM should drive the LD at 100% when you have signal input, so you should be hitting the full forward voltage for your set current.

More info on the driver would help. TTL isn't always 3.3V, sometimes (at least with laser drivers) they expect 5V. If it's an analogue modulated driver it expects 0-5VDC signal input, so a 3.3V PWM signal won't get you to full current. If it's analogue you'd also be as well building a low pass filter to convert your PWM signal to analogue. Or just straight up drive it analogue.


Maxed out my PSU on that test but have cranked that load up to 16A with a different unit and let it run for an hour. Got a little toasty, but not so much so that I was concerned. Ignore the doubled up wiring, only had #18 or #20 on hand at the time, not quite beefy enough to go to the full 20A.

See responses in red.
 
Last edited:

alessnilsen

Active member
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May 20, 2013
Messages
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Points
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I found the driver was defective, it just quit working, I'm already dealing with the seller for a replacement one.

When possible I'll update this.

Thanks for the help! 😄
 




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