Constant current through a load independent of its resistance

Discussion in 'General Electronics Chat' started by unseensoul, Jun 29, 2009.

Dec 13, 2008
22
0
I tried several different circuit configurations (ie. current mirror, howland's current source, etc) to achieve a constant current through a load independent of its resistance but no success. How is this possible? It doesn't make sense to me...

For instance, I tried this circuit configuration - http://www.falstad.com/circuit/e-howland.html - but the current load is affected (it changes) as the load resistance is changed which it shouldn't?! What's happening in here?

By the way, do you know any feasible circuit configuration which will provide me a constant current through a load independent of its resistance?

2. R!f@@ AAC Fanatic!

Apr 2, 2009
8,754
760
How do u do that man, it's really cool (Simulation thingy)
Pls tell

Rifaa

3. steinar96 Active Member

Apr 18, 2009
239
4
In order to achieve this without violating nature law of V = IR you need a circuit that constantly raises the voltage to keep the current magnitude at where you want it to be.

You can't violate physics. So in order to "force" some amount of current trough a circuit you need a circuit that senses the current magnitue and increases the voltage until you have achieved the current magnitude you want. Most likely that will destroy conventional circuits if they are designed to run on lower current then you are trying to force into it.

4. R!f@@ AAC Fanatic!

Apr 2, 2009
8,754
760
I was playing with the circuit...coooool!
As for ur problem, there will be no current via load when u by pass it buddy.
The current will chose the lowest resistance and since a close switch has no voltage drop, the load has no voltage across it, no V, no I in load
Get the point

Rifaa

5. beenthere Retired Moderator

Apr 20, 2004
15,815
282
A constant current source should do that - http://en.wikipedia.org/wiki/Current_source

Remember that I = E/R, so the load resistance has to be within limits. As R gets larger, E has to rise in order to force current. As R gets small, the ability of the source to supply current becomes limited. Both the voltage and current available to a constant current source are limited, and so therefore is the upper and lower value of the load.

Last edited: Jun 29, 2009

Dec 13, 2008
22
0
The circuit configurations I've used are regarded as typical constant current sources so they compensate any loss/gain within some limits, right? Well, it didn't work for me... I was trying to get a constant 5 mA which I think is within the limits...

7. John Luciani Active Member

Apr 3, 2007
477
0
I have a schematic of a constant current sink circuit at
http://tinyurl.com/6cbn6h