Variable current source that can handle negative current als

variable current source

Hi. I cannot make up a functional current source that works for both negative and positive currents.

For either positive OR negative currents I can always put together an opamp to a bjt (or fet) that have a emitter resistor to ground with back coubling to the opamp from the emitter on bjt.

I tried to draw some design, but I just come up with two independent current sources that must have their own load. I want to have ONE load resistor and a current generator that can apply both negative and positive current to it.

I guess I have to think over my first design idea all over again, but don't get any idea how to solve this. Later on, I'm planing to use this for lab purposes, so the "load resistor" is only to test that the circuit will work in practice.

Any ideas?

prototyp_v1.0

Just google for "bidirectional current source". Already the first page of a few million answers (actually the very 1st one) will provide several practical suggestions.

negative/positive current source

Thanks. I found a lot of circuits that might work.

Now the only problem is to select what circuit to use (no - it isn't really a problem )

positive or negative constant current source

I found that it wasn't that many circuits out there that really was what i tought it to be.

Picture below shows a LT1990 chip. Question is, is the LT1990 behaving like a Instrumentation amplifier?
If so, I should be able to make this current source from any regular Instrumentation amplifier.

Beside of that I have designed a circuit that could potentially work, but it require two instrumentation amplifiers and one regular opamp. The less number of opamps used the better it is.

negative current source

Prototyp_V1.0 said:

Picture below shows a LT1990 chip. Question is, is the LT1990 behaving like a Instrumentation amplifier?

Click to expand...

Yes, very similar: It's called a "precision differential amplifier with a very high common mode input voltage range", s. dataSheet (p. 1) below.

Prototyp_V1.0 said:

If so, I should be able to make this current source from any regular Instrumentation

Click to expand...

Sure. However if you can relate your control voltage to the circuit GND, you even don't need an Instrumentation Amplifier, a simple OpAmp then will do the job.