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Old 11th September 2002, 02:02 PM   #1
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Default 12Amp constant current source: OT

Hi Guys,

I need to put 12A through a small piece of metal (for soldering). Thought of a mosfet constant current source. Does anyone have asome parts and configuration for this application. Could use low voltage.

Thanks

Dale
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Old 11th September 2002, 02:12 PM   #2
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Greetings

Can you tell me more about what your application is? I think I can help you...

Cheers

Anthony E Holton
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Old 11th September 2002, 02:27 PM   #3
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Hi Anthony,

Basically, we are trying to solder a very small ferrule (metal cylinder) of about 15mm onto a metalized optical fiber (OD is 125 microns). There is a small solder ring that will be placed on top of the ferrule. The plan is to have two electrode collars from top to bottom and pump about 12A of current through (.09 Ohms) and heat up the ferrule, thus flowing the solder inside of the ferrule.

Got that?

We have modeled a CCS using some mosfets and a bipolar transistor. My peer thinks that I'm crazy to use audio amps as a knowledge source. Now, he's convinced.
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Old 12th September 2002, 01:11 AM   #4
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Hi Dale

This is most likely very similar to your circuit.
However it works and it would be very easy to implement.

Let me know what you think?

Regards

Anthony
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Old 12th September 2002, 02:52 AM   #5
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Default Let's pretend it's 1885...

If it's just a one-off job, why not use a 12v car battery and a 1 ohm 150 watt resistor? The current won't quite be constant to the tenth decimal place, but you may be able to get useable results.

GP.
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Old 12th September 2002, 03:35 AM   #6
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You've got a good point, Circlotron. On the other hand, I did just ask for somebody to need my obsession with constant current sources (I'm no expert, just crazed). However, what you want is just a little beyond what I've already drawn the PCB for. Most light and moderate requirements would be satisfied by a symmetric complementary arrangement. That may be the case here as well. While not of high precision parts, it can be fine tuned if you aim low and add resistors in parallel to reach your target current. The exact parts are not critical. You may only need two diodes per side for the transistor bias, depending on their forward drop and a few other things. This arrangement has a dropout about equal to all the diodes in series. There's plenty more I could say, but you have one from each camp.
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Old 12th September 2002, 11:38 AM   #7
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Hi Guys,

Thanks for all of the feedback. The circuit drawn by Anthony is very similar to the one we chose. For a piece of automation equipment, we need it to be repeatable and reliable. Also, we need to be able to change the current based on process recipes. We are testing today.

Best Regards,

Dale
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