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Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Hello all, I have been busy getting a new design for a very high current driver done. It will be made using expresspcb and will use a whole board just for the power mosfets + current sense resistors. Another board will have the op-amps on it and both boards linked together with wires. So far, my design will use 3 power mosfets with three op-amps to control them. My biggest concern is heating of the traces. I am using the miniboards. I have both top and bottom sides of the mosfet board used for the power traces. I still dont know how much current this can withstand like this.
My old driver let me experiment a little with things and find things to make improvements. One thing is to replace trimpots with precision potentiometers, as swinging the current up and down SUCKS when done with a precision trimpot and a mini screwdriver. The current sense resistors get HOT! I need to use some super low resistance ones to dissipate less power. Here are the screen shots of the new boards. (Still in the design stage). Feel free to give some tips! Matt
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Ok, so I have finalized my high current board. Would someone look it over and make suggestions before I have it made? I put in some 30A screw terminals and maximized the copper. I will hold off on the op-amp board and just use breadboard for that section since it will see minimal current.
Comments? Suggestions? I hope to drive a laser diode past 40amps with this and have it all be stable. Each Mosfet is overkill, but has low thermal resistance and low on resistance as well as works well at 5 volts. 3 ought to spread the current around a bit.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Electroholic wrote ...
Dedicated ground return wire for the feedback wires?
Im not sure what you mean exactly...The feedback for the op-amps from the current sense resistors are from wires to be connected from the labled spots (2,4, and 6)
I am also using both sides of the board to max the copper usage. Could this create dangerous capacitance? Or, should I be fine? Thanks! Matt
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Oh okay I think I see what your saying. I will tie opamp board negative to negative of the mosfet board. Maybe that will help? Alot of current will be flowing...maybe I should sim.that somehow? Pspice may be in order... matt
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
looks sweet
I actually might need to build one of these bad boys, I was doing hot wire cutting and managed to fry my 100a linear regulated supply (all 151lbs of it) from the emf kickback It kindsorta stills runs, but I am not hooking any laser diodes to it. Really I want to get a buck converter working, but just don't see when I am going to find time to do it.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Thanks for the compliment! It DOES look nice huh?
Thats sucks about the linear regulator! But that may be a blessing in disguise. 151lbs is awfully big! Even for 100A. I would deffinately go the flatpac route. I talked to an engineer for Vicor about using a 5volt 40A flatpac for laser diodes. He obviously doesnt specialize in lasers, but knew that ripple and transients are bad for them. He thinks these SMPS will do fine. He said they regulate very well. He didnt seem to know much about the turn on and turn off behavior of them though. (Which is super important). A few people on Alt.lasers said they ripped open some Spectra Physics laser diode controllers and found vicor power supplies controlled by a bank of mosfets. (Basically what I have). They all tend to agree that this route SHOULD work fine.
If Spectra Physics thinks a flatpac and a mosfet bank is good for them, then its good for me too!
The great thing about these boards I made are that they ought to be able to be doubled up for even more current control. I could use two boards to control a sh*t ton of current, right? I really dont even plan to go past 40A though, but overkill couldnt hurt.
Right now the op-amps are all sitting on a breadboard. Once I veriy that this is a good design, I will use expresspcb to pimp out an op-amp controller board!
Now for the hardest part: Finding a suitable heatsink and drilling/tapping the damn holes for screws. (I really hate that!).
Could someone help with another question? I am trying to figure out how much power everything will dissipate. The laser diode and current sense resistors are easy, but what about the mosfets? The supply is 5volts, but is that dropped evenly across the circuit seeing as this is a constant current circuit?
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High Current Laser Diode PSU
It kindsorta stills runs, but I am not hooking any laser diodes to it. Really I want to get a buck converter working, but just don't see when I am going to find time to do it.
