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Old 2nd August 2007, 09:50 AM   #1
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Default Constant current source, am I missing anything...

I want a ccs variable from 1.6 to 1.8A, a little more than a single LM317 can supply. The circuit should be simple and cheap. So I came up with the design shown. I know there are higher current regulators, but they have more disadvantages.

Is it alright or am i missing something?
Nothing to do with audio.

Gajanan Phadte
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Old 2nd August 2007, 10:47 AM   #2
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I don't think it will work. The bottom one will be supplying all the additional current when set to the 1.6-1.8 amp range.

Have you considered an op-amp, buffer transistor and current-measuring resistor?
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Old 2nd August 2007, 11:06 AM   #3
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The lower IC is supposed to supply the difference.
I will construct and find out.

Gajanan phadte
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Old 2nd August 2007, 11:44 AM   #4
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Should work OK. The nice thing with current sources is that you can just connect them in parallel. The Zout of each prevents the other to supply current into the other source. I think your circuit will work as required.

I actually think you don't need the OR-ing diodes.


Jan Didden
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Old 3rd August 2007, 04:07 AM   #5
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Janeman wrote
Quote:
Should work OK. The nice thing with current sources is that you can just connect them in parallel. The Zout of each prevents the other to supply current into the other source. I think your circuit will work as required.

I actually think you don't need the OR-ing diodes.

Jan Didden
I tested and it works.

National recommends 0.2 ohms at the output when paralleling the two 317s and mine are over 1.3 ohms. I will try without the OR-ing diodes.

In the final circuit, I will keep the diodes, in any case, for preventing catastrophic results in case one 317 fails.

Gajanan phadte
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