BlackBuck 8M 8A modulated driver with two NDG7475 520nm diodes

[Minamoto Kobayashi]

Hi forum!
I'm near to terminate a very very beautiful and complex handeld with two 1W greenies, but I need help.
So, I have a pair of blackbuck 8M 8A drivers set at 4.5A each, but I want to use only one set at 2.3A with two 520nm NDG7475 diodes in series.
I will use also the external trim pot to vary the output from min to the max power and viceversa.
My question is: can this device drive both the diodes in series at 2.3A (and I suppose at 10V) without any kind of issues?
And .. what kind of test load I must build to preset the driver at 2.3A to work correctly with two NDG7475 diodes in series?
Thanks in advance ... :thanks:

 

[94Z28]

I am wondering myself of the Vf of these diodes, I have one as well but I haven't hooked it up yet. This is my most expensive diode yet, and I will not rush through this build no matter what. I will most likely drive mine at 1.8 - 2.0 to ensure it has a long life, I want green for beam not for power anyway.

I have researched about the topic, and all I ever have seen is "low VF" for this diode compared to other green 520nm diodes; either way, I would set the test load to twice as much since you are using two diodes on one driver.


/edit > Also, don't forget.. this driver needs a heatsink for sure after about 2.5-3.0A or if you run it for extended periods the NTC thermistor will begin to decrease current/shut off the driver.... If you bind it with the LD's anyway(2x NDG7475 at max current will seriously generate some heat, by my calculations you will need atleast 1lb of aluminum to shed the heat!)

Also, the datasheet says working voltage of 4.6v ; therefore you may need 9.2v to run them both. However this is just a theory and i'm talking out of my arse right now as this is all theory for me still, until I test the whole thing for my RG:Y monster build. I am almost done with the lower-scale project though only missing one piece to fire her up (PBS cube for red 2x LPC-846)

https://drive.google.com/file/d/0B_6-KC5wFXIJeUQySklvNEt4bHc/edit

 

[paul1598419]

At 1.8 amps each the Vf should be about 4.8 volts, so for two in series that's 9.6 volts. Depending on the driver you will probably need 11 to 12 volts, or three Li-ion batteries. Hope that helps. At 2.3 amps for both, that would be about 9 volts total Vf. I think you would still need three Li-ion batteries, though.

 

[Minamoto Kobayashi]

Hi.
I spoke with Mr. Wossee and he do not suggest me to use two diodes with one driver, it could become unstable.
But also if I would to put two diodes in series, I will not have enough place in the battery compartment to put another cell to reach the needed 10+V, so the topic is closed ...
I will use two independent drivers and use a double pot like this:

6pcs 10k ohm 103 B10K Double Potentiometer Linear Pot Rotary new | eBay

to vary the output power in both the LDs together.

I have a question about the test load: x-wossee suggested me to put 7 rectifier diodes in series to obtain the right load (7x0.7=4.9V), and then connect the diodes to a lab power supply , turn to 0 the current and slightly increase it until reach the desired current (in this case, 2.2A).
Is this the right procedure or I can do something more precise?

x94z28:

The build will have a generous copper turret locked on a nice aluminum support, so the diodes will have enough cooling material to dissipate the heat.

 

[paul1598419]

Since you also need a resistor, usually a 1 ohm to measure the drop across it to know the current level, add the 2.2 vols, if you are going for 2.2 amps to the series of diodes to reach the Vf. So, Vf-2.2 VDC= Number of diodes X 0.7 VDC. So if the Vf is 4.9VDC, then 4.9-2.2=2.7VDC. 2.7/0.7= ~4 diodes. The 1 ohm resistor will be in series with the rectifiers and is put at the cathode of the last rectifier in the series.

Edit: I sent you a message from the PM you sent me. Since you are going for 2.2 amps current to the laser diode, you will need to heat sink the output device on your driver board also. These drivers are never 100% efficient, so they will get hot and the heat needs to be dissipated.

 

[Alaskan]

Be careful with your wire lead lengths, I had a driver set to 2,4 amps to drive a 1W 520nm laser diode but due to using wires which were too long to the diode, the current was much lower. I also had a problem with the wires to the battery being too long too, can cause your current to be much lower than what the driver was set to produce, if you had them preset.

 

[Minamoto Kobayashi]

Hi Alaskan!
I had this suspect from the beginning! In fact were used long wires in this build.
Now I'm replacing both the drivers with the 8A modulated buck drivers (with external pot regulation) @ 2.4A each while using shorter cables with larger diameter.
This is a very complex build. Luckly I have CDBEAM777, You, Paul1598419, DTR and x-woosee to support me and this craziness LOL.

Richard.

 

[paul1598419]

Looking forward to end result. Good luck.

 

[Alaskan]

Low gauge wires will make up for longer lengths, but I don't think I am telling you anything you are not ready changing.