Electronics > Beginners
Searching for a component that increases resistance with voltage
Etesla:
Hi all, I am in search of some component that acts sort of like a reverse zener diode. I need it to have 'infinite' resistance above voltage X, and act like a short circuit below voltage X. I'm not looking for a circuit that has this functionality, I'm looking for a single component. I don't think such a component exists, but I'm coming to you guys to double check. The closest thing I can think of is maybe a weird PTC thermistor of sorts??? but I would like this device to be voltage driven, not temperature driven.
Yansi:
This is called negative resistance. There is way to many possibilities to achieve and study this.
You can start with just an opamp and a couple of resistors.
schmitt trigger:
Let's look at your requirements for a moment.
While the behavior of becoming completely open circuit above a certain threshold is fairly straightforward, let's consider your following statement:
...and act like a short circuit below voltage X.
If the device is indeed a dead-short, or an extremely low impedance, when you attempt to increase the voltage, Ohm's law indicates that current will also increase.... in this instance it would to sky high values.
Lets assume that you use a beefy mosfet with only 10 milliohm Rds. And you want this circuit to go open circuit above 10 volts.
Well, to raise a 10 milliohm impedance to 10 volts, 1000 amps would require to flow!
tggzzz:
--- Quote from: Etesla on August 29, 2019, 05:29:58 pm ---Hi all, I am in search of some component that acts sort of like a reverse zener diode. I need it to have 'infinite' resistance above voltage X, and act like a short circuit below voltage X. I'm not looking for a circuit that has this functionality, I'm looking for a single component. I don't think such a component exists, but I'm coming to you guys to double check. The closest thing I can think of is maybe a weird PTC thermistor of sorts??? but I would like this device to be voltage driven, not temperature driven.
--- End quote ---
So, you want a component where 0A flows and there is 0V across it. Then you increase the current to 1A or 1kA and since it s a short circuit there is still 0V across it.
How do you propose to ever get X volts across it?
MosherIV:
Hey, lets be nice to Etesla! This is the beginners forum.
As the others have suggested, you will not find a single component to match your requirements.
Why do you not want a circuit?
Frankly, it is the only way to acheive what you have asked for.
A simple voltage detector circuit that opens/closes a relay.
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