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Old 08-18-2011, 03:04 PM #17
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Default Re: 100W 808nm Bar <50$

Quote:
Originally Posted by joeyss View Post
You guys might want to watch this.

50 808nm 1W HIGH POWER BURNING LASER DIODE DPSS GREEN | eBay

Only $37 after a few bids. Even if it's $200 dollars by the time it ends that's
only $4 per diode.
FYI - That's more huurersciences stuff.

Quote:
Originally Posted by bhwollen View Post
Would that actually work? lol
I can't see why not.

Quote:
Originally Posted by benmwv View Post
Buy seriously, I remember somewhere on here seeing someone talk about using a mosfet as a current sink. Don't remember how exactly but I'm sure it wouldn't be very hard to find. You should be able to find some mosfets able to handle that current, maybe parallel a couple.
Maybe this?
Merghart.com - 2 Transistor current source


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Old 08-18-2011, 08:46 PM #18
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Default Re: 100W 808nm Bar <50$

Well my understanding is that you simply need to use a potentiometer as a voltage divider into the gate of the mosfet. I'll run a simulation.

Ok here is a simulation I made in iCircuit (anybody with an iPhone NEEDS this, don't think it's on android though ). What we've got is a 5v supply, a 10k potentiometer, a 40A mosfet (highest it supports), and an LED which is in place for the diode bar:


Here are the current readings.
at 1/4 turn of pot:


1/2 turn:


3/4 turn:


Full turn:


I have never made this circuit in real life, especially not on such scale but I believe it should work. Just use two (or more) of that circuit in parallel with the max combined current of the mosfets equal to the max current you wish to drive it at.
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Old 08-19-2011, 03:02 PM #19
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Default Re: 100W 808nm Bar <50$

^I tried that in multisim, and it doesn't work. The pot is way too sensitive, and there is a drastic change in output current with a small change in input voltage.
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Old 08-19-2011, 03:24 PM #20
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Default Re: 100W 808nm Bar <50$

Try using a basic linear regulator chip with outboard passbank transistors. It will require more parts, but if you use enough transistors, you can avoid having to use a huge heatsink.
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Old 08-19-2011, 09:33 PM #21
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Default Re: 100W 808nm Bar <50$

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Originally Posted by Cyparagon View Post
^I tried that in multisim, and it doesn't work. The pot is way too sensitive, and there is a drastic change in output current with a small change in input voltage.
It is quite sensitive, but the circuit definitely works cause I made it (not a 100 amp one, low power) a little bit ago.

The current adjusting basically all happens in the last half of the pots range and it increases on a curve as you go. The sensitivity could be fixed by using a multiturn pot, or adding a resistor to one side of the pot equal to it's max value to change the ratio. So when the pot would start feeding at 0v it's now starts off at half of your supply voltage.

Also, considering the amperage needed I don't think it is exceedingly important to be able to dial it in with mili-amp accuracy.
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Old 08-20-2011, 03:30 PM #22
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Default Re: 100W 808nm Bar <50$

The bigger problem is it is not current regulated.
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Old 08-20-2011, 04:12 PM #23
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Default Re: 100W 808nm Bar <50$

Well basically the mosfet is being used as a high power, low range variable resistor but I didn't think it mattered because he will be using a constant 5v supply.

There probably is a better circuit out there i don't know of, but this is the only I can figure to supply so much current.
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Old 08-20-2011, 06:49 PM #24
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Default Re: 100W 808nm Bar <50$

Even a power resistor would be far more stable. I've heard a stove heating element or even clothes hangers work.
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