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Current Source

01/19/2008 6:03 AM

I need a simple ckt for converting 24v ,14.6A DC to 5v 2mA dc(constant current source)......please suggest me

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#1

Re: current source

01/19/2008 6:08 AM

Can you please explain more about what you want - you can only have 5V @ 2mA (constant current) for a constant load (2500Ω). The general idea with a constant current source is that the voltage will vary as the load varies, to keep the current constant.

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#3
In reply to #1

Re: current source

01/19/2008 7:25 AM

thank you , i have 24v 14.6A PLC pannel supply .using that one I need 2ma constant current source ,Please give me a suggession

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#2

Re: current source

01/19/2008 6:42 AM

Look at National Semiconductor for LM317.

It is a voltage regulator that can be setup as a current regulator. Look in their application notes.

It not very efficient but it works well. You will need a heat sink to dissipate the power absorbed by the regulator if you go to higher currents.

If your load is such as to have a 5V voltage drop on it at 2mA, the power dissipation will be (24V-5V)x2mA=38mW, this is not too bad if you use the TO5 package.

At 20mA or 50mA, the regulator would become quite hot and burn your finger.

The next time I need one, I plan to use a switching regulator in the same way.

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#4

Re: current source

01/19/2008 9:20 AM

You don't even need to use a LM317 just buy a constant current diode from... errrm used to be National.. and that will give you 2 ma approx at a voltage range of 0 to 20 volts.

Dissipation is fine at only 24 x 0.002 = 48 mW maximum.

John.

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#6
In reply to #4

Re: current source

01/20/2008 6:26 AM

Do you mean errm ?

This is from their datasheet, the tolerance is quite wide.

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#5

Re: current source

01/20/2008 1:03 AM

http://cr4.globalspec.com/thread/4504/I-need-1-mA-constant-current-source

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#7

Re: current source

01/20/2008 10:43 AM

A simple circuit is possible

IF you can remove the 14.6A from your input Spec.

Say you have.

Then--

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#9
In reply to #7

Re: current source

01/22/2008 2:36 AM

the 14.6A is from PLC pannel ......ok if I am removing that specification please give me a solution

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#8

Re: current source

01/20/2008 6:28 PM

Another solution: Operational Amplifiers (Op-Amp) - very simple ckt.

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#10

Re: current source

01/31/2008 11:51 PM

Look at http://focus.ti.com/lit/ds/symlink/tl430.pdf

There is an example for a current limiter. this works pretty well and is very easy to make.

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