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# How to control the Voltage, Current and Resistance in a circuit? Answered

i've seen devices which do this but I don't know the name of it?

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## 7 Replies

Lima79 (author)2017-10-18

Use resistors/potentiometer, you can also use transistor/mosfet. If you are some what like me, don't want to learn Ohms law and >Watts law:) trial and error are your best friend.

Jack A Lopez (author)2017-10-16

You've, "seen devices which do this but [you] don't know the name of it...."

So it is a device that you have seen. Like maybe, you saw it on somebody's work bench?

I am going to guess the device you saw was a "lab bench" style power supply, with knobs for constant voltage (CV) limit, and constant current (CC) limit, and also some digital displays that show measured voltage and current, as seen at the output of the power supply. Here are some pictures, via an image search for "cc cv bench power supply"

https://duckduckgo.com/?q=cc+cv+bench+power+supply...

Moreover, I am guessing the part you wrote about, "to control the Voltage, Current and Resistance in a circuit", that part is largely in your imagination.

That is to say, I suspect you are incorrectly thinking it is possible to control those three things independently, but I claim, for real, physical, electrical devices, it does not work that way.

A better way to think about voltage and current, is the notion of an I-V curve,

https://en.wikipedia.org/wiki/Current%E2%80%93volt...

The actual current and voltage that will flow in a circuit, is, like, the intersection of the I-V curve of the load, and the I-V curve of the power supply.

Moreover, this "cc cv bench power supply", this kind of power supply tries to supply constant voltage ( has a vertical line, V=constant, for its I-V curve), or it tries to supply constant current ( has a horizontal line I = constant, for its i-V curve).

Although, practically, it cannot supply both constant voltage, and constant current, at the same time. It kind of has to pick one mode or the other, and which one it does pick kind of depends on which limit the load's I-V curve hits first.

Geometrically, in I-V space, it kind of looks like a rectangular box, or at least like the corner of a box, since the CV voltage limit looks like a vertical line, and the CC current limit looks like a horizontal line.

Also, for this kind of power supply, there are usually some little indicator lights, one for "CC", one for "CV", to tell the user which mode the power supply is actually in, at any given moment.

-max- (author)2017-10-11

Learn Ohms law and Watts law and you will understand. I have a couple youtube tutorials for exactly this stuff.

steveastrouk (author)2017-10-11

Its not Watt's law....

iceng (author)2017-10-11

That is a relieve to hear because I never heard of a watts law.

iceng (author)2017-10-11

A potentiometer is a variable resistor which lets you adjust through Ohms law the voltage and current in a circuit... See it work

https://www.wikihow.com/Wire-a-Potentiometer

Voltage = Current x Resistanceor

Current = Volts / Resistance in ohms

Resistance = Volts / Current in amperes..

See the actual component and a schematic symbol below.

Downunder35m (author)2017-10-11

I fail to understand your question.