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Anonymous Poster

current source circuit

06/30/2008 4:41 AM

hi,

i would like to ask on how to build a constant current source circuit base on a common collector configuration?

or just simply a normal current source circuit powered up by either 5V of the microcontroller or 9V from the battery... i need a variety of current source.. 1mA, 10mA, etc..

by the way im building a transistor tester.. any comments or valuable ideas would be appreciated.. as i'm having problems with the testing circuits..

thank you^^

tina
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Electroman
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United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#1

Re: current source circuit

06/30/2008 6:37 AM

I would agree with John, the 117 series would do the job nicely and have all the built in safety circuits...

For low currents though, less than 10 mA, the accuracy will be a bit naff and variable with temperature, but if that's okay its the easiest way.

John.

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bhankiii
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Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: El Lago, Texas, USA
Posts: 2639
Good Answers: 65
#2
In reply to #1

Re: current source circuit

06/30/2008 9:42 AM

For low currents, insert an op amp in the feedback to the adjust pin, in a voltage follower configuration - that still feeds back the voltage, but keeps the adjust pin current out of the output. The LM117 is only good down to a few milliamps.
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Randall
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Join Date: Aug 2005
Location: Hemel Hempstead, UK
Posts: 5826
Good Answers: 322
#3

Re: current source circuit

07/01/2008 6:10 AM

Use this:-

But have R1 switchable between different values: 5K for 1 mA; 500Ω for 10 mA etc.

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