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Zero Cool 27th August 2012 03:16 PM

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?

EUVL 27th August 2012 03:20 PM

See TL431 datasheet. Fig.32.
http://www.ti.com/lit/ds/symlink/tl431a.pdf


Patrick

Zero Cool 27th August 2012 03:53 PM

I will take a read. I think I may have some of those? I will have to look

CharlieLaub 29th August 2012 05:34 AM

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:
http://upload.wikimedia.org/wikipedi...nstCurrent.svg


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

EUVL 29th August 2012 06:48 AM

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.


Patrick

jcx 29th August 2012 07:06 AM

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

abraxalito 29th August 2012 07:20 AM

Quote:

Originally Posted by Zero Cool (Post 3141698)
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.

PaulBysouth 29th August 2012 07:51 AM

1 Attachment(s)
A depletion mode mosfet, like the DN2530 or DN2540, will make very good current sources up to about 100mA. See attached drawing.
pb

Zero Cool 29th August 2012 12:44 PM

Quote:

Originally Posted by PaulBysouth (Post 3143920)
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!

iko 29th August 2012 02:11 PM

1 Attachment(s)
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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