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Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
All great ideas. Im at the point where I cannot stray too far off the path. (just paid for some boards to be made) Those transistors sound promising, but I need t0-247 devices since the boards are made for such. My op-amps take 7volts max as well...I will check out vishay to see if they have something better.
Ill keep you all updated! This project seems pretty promising for all laser diodes.
EDIT: While looking for new MOSFETs with lower Vgs requirements, it occured to me: I could put a 6 volt regulator on the 12 volt supply to power the op-amps/mosfet gates. No? So here is my setup: Ive got a dual flatpac supply consisting of a 5volt 200W supply and a 12volt 200W supply. The 5 volt supply can be trimmed down for the laser diode power (as low as I can get it keeping in mind there will be voltage drop from wires). The 12volt supply will power the TEC, cooling fans, and the op-amp/mosfet gates (via 6volt regulator). How does this sound? I will tie the negative of each supply together. Thumbs up? matt
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
I tried out the setup according to my plans and all seems fine. (SEEMS) I was able to trim down to 2.5volts (didnt try to go lower) and I drew over 25A! Yay! Also, the heatsink wasnt near as hot. It took it a few minutes to get hot and this was without a fan powered up for it. (No diode or load either). I suspect heating will be even less with a load connected.
I will now begin planning a new board dedicated to control. 3 op-amps for the 3 mosfets. A precision voltage reference. A regulator set for around 5volts... Here are the screen shots of the board. (I plan to move some things around still, but this is about what I am sending to expresspcb). There is still some hissing. No idea what thats all about. Ive got some short fat wires in place for carrying large currents. I will need to scope the output and sacrafice some cheapo laser diodes (bare) to be sure its just nothing. (Maybe just some transformer or inductor winding within the flatpac?)
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
As you trim down the Vds, you will probably have to increase Vgs more to keep the Rdson low enough. I would probably get some higher voltage opamps and run the opamps and gates from the 12V supply.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Electroholic wrote ...
As you trim down the Vds, you will probably have to increase Vgs more to keep the Rdson low enough. I would probably get some higher voltage opamps and run the opamps and gates from the 12V supply.
Hello, Have a look at the transistors data sheet: About half way down, they have some charts. From the looks of things, it seems that the transistors ought to be happy with a Vds of only 2.5volts and a Vgs of 5volts. Or am I mistaken? (still an amateur at things like this). Anyhow, I need to stick in a shunt or something and figure out the max current I can draw.
Any ideas as to the hiss from the flatpac? Thanks! Matt
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
SUCCESS! I hooked all the stuff up as planned and tested it out. The heatsink barely gets warm now with the voltage trimmed down to 2.5volts (actually needs 2.8volts when a high power laser is connected). No more hiss either as I replaced a "ground" wire with a big fat short 10awg wire to connect the two power supplies. Before this, there was ALOT of ringing as seen on my scope. NASTY looking stuff (nasty looking 8 volt spikes). Now its a slight ripple. (The vicor engineer did say to expect a slight ripple. (Looks to be a 1vp-p ripple). I hooked up my 40watt laser diode and gave it 30A. The TEC keeps it very cold (need to get one of those controllers ). A focusing lens from another laser assembly focuses the laser down to less than a millimeter (just guessing). MAN what power this has! White objects burst into flames. I made a rock heat up and begin to act like a sparkler. A youtube video is coming soon. Check back for the link later. Now that things seem to work fine, I need to get a board made for the controller stuff and put it all together in a nice compact package.
EDIT: Excuse the messy room! I dont spend much time here due to aggravating roommates! Matt
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Harry wrote ...
Well done, lad! We can always discover a way and work things out if we keep at it!
Thanks!
I had an idea that may work for controlling the TEC temperature. Instead of the sophisticated controller, I wonder if I could sneak by by trimming the 12 volt supply down some. This would reduce power to the TEC and thus its ability to remove heat from the laser diode. Seems funny now that the problem is the laser getting too cold. Both extremes will kill it. Im not sure how far I can trim down, (I know it cannot be trimmed down to 50%) but It seems that a few volts might do the trick. Since I dont need to be at a specific temperature, and this idea would fit on the board I will be making, I thought id run it by everyone (that cares). Wouldnt be "elite" but it would save money and be easy to use. Matt
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Thats great! I love how you can see the beam path. Trimming may work. If you put a smaller heatsink on the hot side, that may also prevent it from getting too cold. Good luck.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
Good to hear you got it working. One scary setup you got there. TECs are kinda like laser diodes. To achieve good control with TECs, you would be better off with a variable current source, I say hook it up to one of your other "laser PSUs" and control the current that way.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Electroholic wrote ...
Good to hear you got it working. One scary setup you got there. TECs are kinda like laser diodes. To achieve good control with TECs, you would be better off with a variable current source, I say hook it up to one of your other "laser PSUs" and control the current that way.
Thanks for the tip! I will hold off on anything for now as it seems the TEC needs its strenght when running around 30A through the laser. It gets cold, but nothing like it does at half the current. I may just use a lower power fan to bring the temperature up some. (Its forming condensation). Here is a new video! Had someone standing by with a fire extinguisher! Matt
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High Current Laser Diode PSU
