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variable constant current source?
variable constant current source?
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Old 27th August 2012, 02:16 PM   #1
Zero Cool is offline Zero Cool  United States
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Default variable constant current source?

I would like to build a variable constant current source for experimenting with various stage topologies. I would like something that is variable from say 1ma to more than 10ma maybe as high as 100ma?

any suggestions?
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Old 27th August 2012, 02:20 PM   #2
EUVL is offline EUVL  Europe
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See TL431 datasheet. Fig.32.
http://www.ti.com/lit/ds/symlink/tl431a.pdf


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Old 27th August 2012, 02:53 PM   #3
Zero Cool is offline Zero Cool  United States
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I will take a read. I think I may have some of those? I will have to look
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Old 29th August 2012, 04:34 AM   #4
CharlieLaub is online now CharlieLaub  United States
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variable constant current source?
This might be of interest to ya, mate!

Constant Current Source/Load (LM317) | The Paranoid Troll

In general, the LM317 IC is used like this:
Click the image to open in full size.


I did a quick Google search, based on my memory of seeing this in a data sheet once upon a time. I am sure that there are other resources about this out there.

-Charlie
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Old 29th August 2012, 05:48 AM   #5
EUVL is offline EUVL  Europe
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A more modern alternative to LM317 for low current:
LT3092 - 200mA 2-Terminal Programmable Current Source - Linear Technology

I also use LM317 or LT1083, etc., but usually for current above 500mA.


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Old 29th August 2012, 06:06 AM   #6
jcx is offline jcx  United States
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while regulators can be hacked to give CCS they often have limited bandwidth

purpose designed chip:

LT3092 - 200mA 2-Terminal Programmable Current Source - Linear Technology

can also make "Howland Current Pump" with op amps or power chip amps depending on requirements

http://www.ti.com/lit/an/snoa474/snoa474.pdf
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Old 29th August 2012, 06:20 AM   #7
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by Zero Cool View Post
I would like to build a variable constant current source for experimenting with various stage topologies. I would like something that is variable from say 1ma to more than 10ma maybe as high as 100ma?
I would have suggested LM317 like the others but I think down at 1mA it won't regulate properly. Also as jcx says the bandwidth is somewhat limited - watch out for the parasitic capacitances.

A solution that will encompass 1mA would be an opamp driving the gate of a MOSFET with a resistor to a power rail from its source. -ve input of opamp to source, +ve input of opamp you feed a voltage which defines the current you want. Choose the resistor to suit the current range you require. You need an opamp whose CM input voltage goes down to the -ve supply with an N-channel MOSFET - this makes a current sink. For sourcing, a P-chan MOSFET is called for and the opamp needs to allow CM voltages up to the +ve supply.
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Old 29th August 2012, 06:51 AM   #8
PaulBysouth is offline PaulBysouth  Australia
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A depletion mode mosfet, like the DN2530 or DN2540, will make very good current sources up to about 100mA. See attached drawing.
pb
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File Type: jpg Adjustable-Current-Source.jpg (109.7 KB, 410 views)
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Old 29th August 2012, 11:44 AM   #9
Zero Cool is offline Zero Cool  United States
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Quote:
Originally Posted by PaulBysouth View Post
A depletion mode mosfet, like the DN2530 or DN2540, will make very good current sources up to about 100mA. See attached drawing.
pb
I have plenty of DN2530's on hand. I like that solution. a little limited at only 25ma but that will work for most things. I will review the others, thank you everyone!
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Old 29th August 2012, 01:11 PM   #10
iko is offline iko  Canada
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variable constant current source?
Why not something simple like this. Almost any general purpose npn and power mosfet will do. Play with R1 and R2 to get the current you want.
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