The Big Green Thread (I'm gonna regret posting this in the morning)

[shrad]

Maybe there's room for an open source community project there...

Steve do you have other circuits in your collection which could, assembled together, form some kind of "uber driver"?

In my attempts to achieve reliable high side current sensing with N-mos device, I always had modulation issues so I finally dropped on that and told myself I'd better buy an off the shelf driver

But I've got so much parts in my bin that a generic discrete design (ie LM358 + IRF450 thing) would be a perfect thing to have... anyway, as new diodes get insulated bodies, I don't think there is a real need of high side driving since even a pump diode will be insulated by a TEC in most cases

Apart from this, maxim-ic makes some nice development kits for TEC controllers for as low as $25/p which consist of a 0.01°C control loop with voltage setpoint and CTN/voltage sensor

[VDX]

... I'm driving high-power IR-diodes with currents up to 9Amps with LM317/LM338/LM350 and PWM-switching (opto-coupler) them with a MOSFET.

Found a simple analog driver with up to 1MHz driving range, that can be used for the same LM-array, so no problem to build a driver with TTL or analog input and high output currents ...

Viktor

[shrad]

While it may be suitable for high power second hand diodes for engraving, LM317/LM338/LM350 are not suitable for this as they suffer stability/thermal runaway issues, and PWM would interfere with show modulation, I think

[VDX]

... I'm using them in current regulator mode parallelized up to 5 of them (different types and set currents for predefinable current-steps) and a big heatsink without remarkable issues - here (under "4. power-source:") some images of the first protptypes: http://reprap.org/wiki/Laser_Cutter

Have an adjustable PS with 8x LM317 supporting 2-30Volts @10Amps and too didn't notice voltage shift over longer time.

Could be my coolers are a bit bigger than needed ... or connecting the coolers to the steelframe housing with even bigger thermal mass helps me with thermal stability issues?

... or my 'rule of thump' - don't use a LM317 for more than 1Amp?

And for the PWM - i'ts only intended to 'finetune' between the coarse predefined current steps I've setting by switching the single LM's to or from the bank.

I'm using them in CW-mode and the PWM-ability is meant for fine power adjusting when driving vector curves to avoid overshoots at slower speeds (as seen in the images) ... but hadn't done this until now.

With the 1MHz-analog driver this should be even better controllable, so will assemble one of them soon for testing ...

Viktor

[steve-o]

R3 and R12 must be Kelvin connected.

THANK YOU STEVE .. I asked an "engineer" where I work today if he wanted all the grounds in a Kelvin connection and he said " a what?".. I said "where all the grounds go to one point" .. he had no idea what I was talking about.. he was asking an administrative assistant how to hook up electrical grounds .. it was ridiculous ..
Thank you for posting that .. I looked up Kelvin connection on wiki, got only the temperature scale ...

[macpod]

I have used soapy water with success and a sharp carbide cutter. It was quite a surprise to learn about copper's machining qualities on the first go.

[badger1666]

I guess this project came to a stop ? Been no updates for a while

[planters]

I guess this project came to a stop ?

No. Not at all. I just have been very busy. All of the components have been purchased and except for the cavity mirrors have been delivered. The free space pumps are running and just today I have finished evaluating about a dozen different lens combinations and I have some very good results with beam size, shape and positioning. These IR beams are a little spooky. They are faintly visible, but HOT and have to be manipulated while watching a video monitor. The optical mounts are all (with the exception of the vanadate support) installed on an optical bench.

Steve is approaching this a little differently starting with fiber pumps, but I'll leave the details to him.

[dar303]

Very cool, looking forward to pics of well behaved green photons marching in a row!

[planters]

We have ignition!

Not a lot of time to discuss and the system needs characterization, but late last night after 20-30 min. of tweaking optical alignment and... boom the video monitor saturates. I quickly turned the pump down to 300mW (bias setting) and a hair thin sparkling beam could be seen transversing the inter-cavity "Z". Details to follow.