Multiple diode question

[yaddatrance]

Some more pictures of the fiber. Yeah, The fiber is centered pretty
accurately in the SMA905 connector so you just have to
align the fiberfed lasers once and then you can just mix'n match
lasers and scansystems... It's the only way to run the bigger lasers
like the Sabre and the 171s...

[allthatwhichis]

You da man! Looks like you could eat off any surface in that room also... Is that your kitchen?

[p1t8ull]

All this and no pictures...

It needs a bit more work yet, but I have finally got something together. I just need to mount the PBS and mirror and also make a base/enclosure. The finished module will have a footprint of 50x85mm and be 35mm high.

The original plan was to make 3 of these (6 diodes) and combine into one beam using mirrors/mounts for a >500mW module, but after testing the diodes and getting a bit more power than expected, I have decided to stick with these two for now, as combined they produce just about the level of power I need for the RGB projector I'm putting together at the moment.

Thanks for all the input re. wiring multiple diodes in series, very enlightening.

Pit.

[allthatwhichis]

Nice! That doesn't get warm?

[p1t8ull]

Nice! That doesn't get warm?

The TEC between the mount and the baseplate keep the diodes nice and cool, and lower the wavelength a few nm's


The only problem (found about 3 minutes ago) is that when the 2 diodes are wired in series, the diodes will only draw a max of 140mA with a 1A capable driver - even with the currrent pot wound round to max. I swapped that driver for a more basic (but still 600mA) one and it maxed out at 115mA

The bench supply feeding the drivers can provide up to 3A and it's getting not getting near that, so the supply is fine. The TEC is disconnected for this test. The diodes work perfectly and ramp up to 300mA+ when wired individually.

Looks like physics get's the last word on wiring laser diodes in series, and it's a big, fat, NO!

Pit.

[steve-o]

What is the maximum voltage of your supply?

[p1t8ull]

What is the maximum voltage of your supply?

The bench supply is variable from 5 - 30v DC, 3A at all voltages. Set at 4.9v as the driver requires 5v - according to the docs.

Pit.

[yaddatrance]

That looks good! I like the jeweling...

P.S. If you really want to run your diodes in series, you'll have to empirically determine what the real max voltage is and guage from the voltage drop of the diode whether you have enough headspace to run both using an increased voltage while regulating the current. Your driver may have caught it right at the transfer point... basically if the voltage due to v.drop on the second diode is too low, then current will restricted.

[steve-o]

Yadda beat me to it..
Basically, you have to run twice the voltage for 2 diodes in series as opposed to the voltage of only one, while keeping the current within design parameters.
Steve
PS --Yeah, nice metalwork.

[p1t8ull]

Thanks Yadda and steve, spot on.
Ramped up the voltage gradually to 6.5 volts & the current soared with it.

Did I mention that I'm an electrical numpty?

Pit.