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Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Hello, I had tried some IRFP9150's and they seem unstable at currents above 4amps. The current goes all over the place (in the 10's of mA). Once I back it down, current levels out. Heating the issue?Crappy wires? (On breadboard still). The TIP42's are also unstable above about 5 amps, but seem to work at 4amps. Current creeps up and down by a mA or so...Seems HARD to control current this way! Larger heatsinks needed? This thing is getting BIG! EDIT: I found some IRF9640 Ptype fets. They work alright it seems. Ive had the laser running 4amps for some time now and all seems fine. Current creeps up and down a little, but nothing insane. I will look for some better mosfets. So for this application, what would be better? Lower in/out capacitance or lower on resistance? The lower the on resistance seems to suggest higher current as well as MUCH larger in/out capacitance. Since my op-amp can only supply 25mA, the in/out capacitance needs to be kept as low as possible, no? Matt
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
Some new updates: I am finishing up an epxresspcb design for a driver using the op-amp and some mosfets. I have been looking over mosfets at MOUSER and found : FQP17P10 I will order some of these and see if they perfom better. (Less heating).
Anyone care to see the expresspcb design before I submit it? Check back later for a video I made of me screwing around with the laser! ( I will edit this posting with a link to youtube for it). EDIT: Here is a video of the laser running. I have a much better video (running at much higher power with much better clarity), but youtube isnt working for some reason. (Cant upload it).
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SIMPLE Laser PSU
( I will edit this posting with a link to youtube for it).