1. Home
  2. ⏚ Electrical Engineering
  3. current limiter / voltage regulator question

current limiter / voltage regulator question

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
Reply to
panfilero
Loading thread data ...
what would happen if you connected the 0 - 5V directly to your 15 ohm load ?
"all" you need to do is scale the 0-5V up to 0 - 30V the 15 ohm resistance will convert the voltage to 0-2 A
perhaps using a single-rail op-amp and a NPN power darlington in common emitter configuration.
Bye. Jasen
Reply to
jasen
you only need a constant current source if you have a varying load such as a battery. with a fixed load a variable voltage supply will be fine .
Reply to
TimPerry
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).
Reply to
Brian Ellis
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.
Reply to
DaveM
Very good observations, Dave. When you don't go through the numbers, it is easy to overlook some of the details.
Item (1): That may or may not hurt the Op, based on what he is using it for.
Item (2). That would probably be a problem.
The "Adjustable Current Regulator" would be okay, if he has a negative supply. At least according to the drawing, he would need a -5 to -10 volt supply, too (even though a very low current negative supply). Or, am I reading it wrong?
I drew a diagram up, look at
formatting link

Reply to
Brian Ellis
IIRC he had a 0-5V input, not a pot input.
here's one way to do it using an LM350 +33.5V --[RL]----[LM350A]---[0.1]--- 0V | 5W | Vin (0-5) --[2K4]---+--[100R]--- -1.3V The silly looking 33.5V supply is needed to accomodate the 30+3+0.2V drop under full load and stat under the 35-1.25V maximum under no load. it works on paper with ideal parts but 1% drift in the part translates to a 6% drift in output,,,,
Bye. Jasen
Reply to
jasen

Further Reading

  • voltage regulator question adjustable voltage needed

  • Hello,ok, I'm looking at the datasheet for a 12V voltage...

  • EV voltage limiter

  • I would like to find/make a (cheap) efficient way to limit a 72V battery pack...

  • Regulator rebuilding question

  • Hi folks,I have 2 old sets of (Prest-O-Weld, Linde, Union Carbide, Purox)...

  • Welding regulator question

  • I connected an oxygen regulator (Victor SR 450) to a cylinder. No hose is...

  • Current limiter for DC motor

  • Hello,I've already made a set of cards that control speed of a small DC...

  • check voltage regulator

  • I've just purchased a 30 year old gasoline engine forklift...I note that the...

  • Voltage Regulator

  • A two volt variation is a .87% regulation which is quite good. The detectormay...

  • sot23 voltage regulator

  • Hi,I am looking for a sot-23 (or similiar size) package voltage regulator...

  • Current / Voltage regulation

  • okay - quick one here - i have a power supply that someone gave to me.current...

  • Voltage and Current

  • Q1) Is it possible that a machine burns out due to voltage drop at itsterminal?...

  • Voltage Drop of Regulator Output

  • Greeetings:I am trying to build a +5V regulator using a LM350K. I am using a...

  • Regulator Gas Compatibility--H2 regulator for CO2?

  • I have salvaged a hydrogen regulator in good condition. I'd like touse it...

  • Building voltage regulator for 3ph generator

  • I have an old 15 KW 3ph generator that is missing the voltage regulator. ...

  • Acetylene regulator sputter

  • My acetelyne regulator sputters and pops when setting and welding. Thesputter...

  • How does a voltage regulator work?

  • Look up the term "shunt regulator".My motorcycles' voltage regulator...

  • Question

  • I'm working on understanding an example problem in order to do a homework...
  • « previous thread

  • How can I build a 2:1 3 phase voltage attenuator from resistors

  • My datalogger is for 600VAC maximum, but sometimes my source is higher like 630V...
  • next thread »

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.