a transistor is a variable resistor

[bertus]

Hello,

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

Textbook for Electrical Engineering & Electronics

These free electrical engineering textbooks provides a series of volumes covering electricity and electronics

www.allaboutcircuits.com

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

Electronics For Dummies : Dickon Ross, Cathleen Shamieh, Gordon McComb : Free Download, Borrow, and Streaming : Internet Archive

What it says on the tin...

archive.org

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

Illustrated Dictionary Of Electronics Stan Gibilisco : Stan Gibilisco : Free Download, Borrow, and Streaming : Internet Archive

Illustrated Dictionary Of Electronics - 8th EditionbyStan Gibilisco

archive.org

Bertus

 

[dragon]

Do you need to read these books still?

 

[AnalogKid]

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]

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:

Folkscanomy Electronics: Books on Electronics, Circuits and Processors : Free Texts : Free Download, Borrow and Streaming : Internet Archive

Bertus

 

[crutschow]

You need to open your mind a little bit!

Sorry, but I don't indulge in mind-altering substances, which you seem to.

 

[willsonwanda]

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]

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]

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]

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]

Read here:

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]

Hello,

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

Bertus

 

[Harald Kapp]

A VDR is a voltage DEPENDEND resistor.

Right, but note that dragon mentioned a VCR.

 

[dragon]

A voltage Dependant resistor is still power controlled.

 

[Harald Kapp]

This thread is leading nowhere, so I'll close it.