"Brian Ellis" <XXbellis350@comcast.net> wrote in message
news:y5OdnZ7dd_VAjCPYnZ2dnUVZ_qmpnZ2d@comcast.com...
"panfilero" <panfilero@gmail.com> wrote in message
news:1170045009.073294.142060@v45g2000cwv.googlegroups.com...
Hello
I need to deliver a variable current between 0-2 Amps to a small load
(15 Ohms).... At first I was thinking about building a current
amplifier..... but after investigating that route again, i think, it's
too difficult to build.
Then I heard about adjustable voltage regulators. And looking through
the datasheet of an LM117, I noticed it had a curcuit example it
called: "Precision Current Limiter" where the output current is
controlled by a potentiometer and can be varied from 0 to 1.65 Amps.
I'm not sure if this is a variable constant current source, but it
kinda sounds like it to me, is anyone familiar with this circuit?
In the "Precision Current Limiter" circuit the current is controlled
by a potentiometer, but I need to control the current with a variable
voltage (between 0 - 5 V), is there such a thing as a voltage
controlled resistor? So that I could use that in this circuit?
any help is greatly appreciated,
thank you
Joshua
Instead of using the LM117 "Precision Current Limiter", use the LM150
"Precision Current Limiter". It goes up to 3 amps. Yes it is a variable
constant current source. You set whatever constant current you want, and
as the load varies, it will maintain that current (provided the voltage
supplying the constant current regulator is high enough).
--
Brian Ellis
FNC-Elcad
http://www.fncwired.com/
What the last poster says is true, and recommendation of the LM150/350 is
good, but in context of the original question, there are problems with
this approach.
(1) The OP stated that he needed to supply a fixed resistance with 0-2
amps. The "Precision Current Limiter will not go to zero amps. It can get
close, but never to exactly zero amps.
(2) The current limit pot that controls the current must be able to handle
at least 2 amps... not an easy task for a common potentiometer.
I suggest that the OP consider the circuit titled "Adjustable Current
Regulator" in the LM150 datasheet for full realization of his
requirements. The additional regulator and negative voltage source in
that circuit lets the output current go down to zero amps, while still
giving good control up to full output current.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters
in the address)
Some days you're the dog, some days the hydrant.
