# a transistor is a variable resistor

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#### bertus

Moderator
Nov 8, 2019
2,855
Hello,

@dragon , You could have a look here to learn the basics of electronics:

Also the following books might help.
For absolute beginners this might be reasonable:

For more understanding of components have a look at this book:

Bertus

#### dragon

Oct 31, 2022
217
Do you need to read these books still?

#### AnalogKid

Jun 10, 2015
2,699
the resistance gets cancelled out.
I understand what you are trying to say, but the way you are saying it is incorrect.

In DC and AC circuits, "cancelling out" something is a specific action, and that action is not what you are describing. A power supply does not cancel anything. However, adjusting the output voltage of a supply, or going from one supply to two supplies in series, can compensate for the consequences that increasing the impedance of an element in a loop has on the value of the current through the loop.
Is there a way you can get a variable resistor with just passive components?

Try this:

Is there a way, using nothing but passive components around a single bipolar transistor, to create a circuit that behaves as a voltage-variable resistance?

No.

With an analog multiplier?

Yes

ak

#### bertus

Moderator
Nov 8, 2019
2,855
Hello,

I have been busy with electronics for about 50 years now.
I have been reading a lot of books on electronics and have been experimenting with electronics too.

The internet archive has a lot of electronics books from beginner to very advanced:

Bertus

#### crutschow

May 7, 2021
584
You need to open your mind a little bit!
Sorry, but I don't indulge in mind-altering substances, which you seem to.

#### willsonwanda

Dec 13, 2022
5
Yes, a transistor is like a variable resistor, in that the resistance between collector-emitter or drain-source is variable. It's like a valve, and either allows current to flow or blocks it from flowing.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,792
Sorry! I mean current controlled variable resistor.
A thermistor is a current-controlled variable resistor: you send current through a thermistor and it gets hot and its resistance either increases or decreases. Any resistor whose resistance is a function of its temperature can also be considered a current-controlled variable resistor. And resistors are of course passive components.

Another device you might be interested in showing your ignorance about is the parametric amplifier. Go Google and noodle on that before disturbing us with any more of your stupid comments. Maybe you can model a parametric amplifier with your Falstad simulator...

#### crutschow

May 7, 2021
584
A thermistor is a current-controlled variable resistor
I think that you are being too loose with the terminology.
The usual meaning for a current (or voltage) controlled device is that a current or voltage is controlling separate, but not necessarily isolated parameter.
I would call a thermistor a temperature controlled resistor (since it's not a function of just current).

#### dragon

Oct 31, 2022
217
You can get these things called VCR's voltage controlled resistors.

but I think I wont be needing them, series connecting power supplies should do it along the "flow line"

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,079
A voltage-controlled resistor (VCR) is a three-terminal active device
Just because the device is named "resistor" doesn't mean it actually is on. So sorry, no pasive device here.

#### bertus

Moderator
Nov 8, 2019
2,855
Hello,

A VDR is a voltage DEPENDEND resistor. Nowerdays they are called MOV.

Bertus

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,079
A VDR is a voltage DEPENDEND resistor.
Right, but note that dragon mentioned a VCR.

#### dragon

Oct 31, 2022
217
A voltage Dependant resistor is still power controlled.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,079

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