Searching for a component that increases resistance with voltage - Page 1
Forum section: electronics / beginners

author: Etesla
author_rank: Regular Contributor
timestamp: August 29, 2019, 05:29:58 pm
content: 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.

author: Yansi
author_rank: Super Contributor
timestamp: August 29, 2019, 05:34:31 pm
content: 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.

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 29, 2019, 06:00:01 pm
content: 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!

author: tggzzz
author_rank: Super Contributor
timestamp: August 29, 2019, 08:27:27 pm
content: Quote from: Etesla on August 29, 2019, 05:29:58 pmSo, 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?

author: MosherIV
author_rank: Super Contributor
timestamp: August 29, 2019, 10:28:58 pm
content: 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.

author: ArthurDent
author_rank: Super Contributor
timestamp: August 29, 2019, 11:24:07 pm
content: A lot may depend on what the 'fuse' will see for voltage and current and whether it has to have no leakage when open or blown. Check this video to see if this is the type of component you're looking for. It is true that this reacts to the load current so if the load current increases as the voltage increases, this might work. Neither a polyfuse or a regular fuse will do exactly what you describe. More information on what you're actually trying to do would be helpful.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 30, 2019, 07:33:32 am
content: Constant current source.Or actually, more exactly -- are you after negative resistance (at high voltage, theaverageresistance goes to infinity), or constant current (at high voltage, theincrementalresistance goes to infinity)?Search on these terms (incremental resistance) to see definition and discussion.Tim

author: tggzzz
author_rank: Super Contributor
timestamp: August 30, 2019, 10:41:04 am
content: The OP has indicated thesolutionhe is looking for, in terms of a device's unattainable ideal V-I characteristics.If the OP would specify theproblemorobjectiveto which such a device might be a solution, we could provide more concrete help.In most walks of life, technical or non-technical, if we know the reason for the question you will probably get a better answer. Either the answer will be more pertinent to your needs, or perhaps it can suggest a better alternative that you haven’t even considered. Don’t ask “Can you give me a lift into town?” Do ask “Can you give me a lift into town, so I can replace my broken frobnitz?”. The answer might be “There’s a spare frobnitz in the attic”, thus saving time, money, the environment – as well as making some space in the attic.

author: martin1454
author_rank: Regular Contributor
timestamp: August 30, 2019, 10:46:09 am
content: Maybe some sort of varistor? They can be hard to find with low enough resistance in low voltage, but can get pretty high resistance in high voltage.

author: KMoffett
author_rank: Regular Contributor
timestamp: August 30, 2019, 03:09:37 pm
content: Isn't increasing resistance with increasing supply voltage the definition of a "constant current" source? But then we don't know what Etesla wants to use this for.Ken

author: grifftech
author_rank: Frequent Contributor
timestamp: August 30, 2019, 03:54:13 pm
content: incandecent lamp

author: ArthurDent
author_rank: Super Contributor
timestamp: August 30, 2019, 04:06:46 pm
content: Technically a relay that pulls in at the voltage of interest and disconnects the load across a set of N.C. contacts would work. The problem is this trip point is probably a little broad and finding a relay to match the criteria will not be easy. A series resistor, which adds a second component, could adjust it somewhat . Once the relay pulls in it will hold until the input voltage drops to a much lower value so you'd have hysteresis.

author: FriedMule
author_rank: Frequent Contributor
timestamp: August 30, 2019, 05:18:10 pm
content: First, I am a noob so please bare with me but there is an optocoupler that do the exactly opposite of what you want, but maybe you could get the optocoupler to control a digital potentymeter?opamp here:https://www.onsemi.com/pub/Collateral/H11F3M-D.pdf

author: soldar
author_rank: Super Contributor
timestamp: August 30, 2019, 09:04:51 pm
content: Quote from: grifftech on August 30, 2019, 03:54:13 pmIndecent lamp can.

author: Kilrah
author_rank: Unknown
timestamp: August 30, 2019, 09:16:59 pm
content: Until it pops

author: Mattjd
author_rank: Regular Contributor
timestamp: August 30, 2019, 10:58:36 pm
content: Quote from: Yansi on August 29, 2019, 05:34:31 pmWhen I saw that thumbnail I thought it was going to be some sort of memristor based thing. It wasn't but it was a circuit made by Chua himself at least.

author: Brumby
author_rank: Unknown
timestamp: August 31, 2019, 08:00:23 am
content: Quote from: ArthurDent on August 30, 2019, 04:06:46 pmThis idea is the closest I've seen to satisfy the criteria specified - and - it has the added bonus of having the infinite resistance/zero resistance characteristic isolated from the trigger voltage.Of course, the criteria specified do have a lot to be desired if we really want to offer appropriate suggestions.Quote from: tggzzz on August 30, 2019, 10:41:04 amIndeed.