What can I use to put inline in a circuit to cut off voltage after it rises to a certain point? - Page 1
Forum section: electronics / beginners

author: dclevy1
author_rank: Contributor
timestamp: May 10, 2017, 05:49:42 pm
content: Something that acts like a circuit breaker but for voltage. I was looking into a voltage regulator but those expelled Heat in the form of keeping the voltage regulatedSent from my SM-N910P using Tapatalk

author: tooki
author_rank: Super Contributor
timestamp: May 10, 2017, 06:19:23 pm
content: MOVs are classically used for this. But you'll probably wanna be a lot more specific as to the application, e.g. what kinds of voltages are we talking? Are such surges expected to be common, or just for emergency protection of singular catastrophes? AC or DC? What are the devices in question?

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2017, 06:23:03 pm
content: You could build something with a relay to open the circuit and a comparator to monitor the input voltage, a few resistors to make dividers, a zener or TL431 reference and a transistor to switch the relay.

author: SeanB
author_rank: Super Contributor
timestamp: May 10, 2017, 06:26:12 pm
content: You are looking for an overvoltage crowbar, used along with a fuse or other protective device to clamp overvoltage. Otherwise you are looking for a transient protector or diode.

author: macboy
author_rank: Super Contributor
timestamp: May 10, 2017, 10:29:49 pm
content: A "crowbar" is a very useful over voltage device, but it may not act as intended by the OP. A crowbar is designed to short the voltage source to ground if the voltage gets too high. If a person wants the source to be disconnected instead then a different type of protection is needed.

author: TimFox
author_rank: Super Contributor
timestamp: May 10, 2017, 11:06:19 pm
content: Typically, a crowbar is used to short out the source to avoid damage to a sensitive load, leaving the source to protect itself (fuse, etc.). A good crowbar can react much faster than a typical series switched open-circuit device.

author: dclevy1
author_rank: Contributor
timestamp: October 25, 2017, 06:06:40 am
content: Okay so I had a lot going on so I forgot why I posted this question but it can still be useful to me. So should I go with a MOV like the first poster said or a crowbarSent from my iPhone using Tapatalk

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 25, 2017, 06:14:04 am
content: Neither, first you should specify what you need a bit more clearly.Do you want the voltage to go to zero once it has reached a certain voltage or do you want the voltage to stabilise once it reaches a certain voltage?What sort of voltages are you taking about. AC, DC, high, low?

author: dclevy1
author_rank: Contributor
timestamp: November 16, 2017, 01:51:32 am
content: Quote from: Mjolinor on October 25, 2017, 06:14:04 amDC voltage and what can I use her either instance. Stabilized or go to zeroSent from my iPhone using Tapatalk

author: IanB
author_rank: Super Contributor
timestamp: November 16, 2017, 02:40:14 am
content: Quote from: dclevy1 on November 16, 2017, 01:51:32 amBut see, these trains here are running at 750 V DC and drawing upwards of 1000 A. So "DC voltage" is a bit ambiguous.If you say exactly what you have in mind as an application, then you may get some useful and specific answers.(If you dropped an actual, metal crowbar across the live rail here it would probably trip the over current protection, but there is likely to be an almighty bang and flash before that happened.)https://youtu.be/XIUDiCjvCxM

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 16, 2017, 09:42:59 am
content: Idea? LTC4380

author: dclevy1
author_rank: Contributor
timestamp: November 20, 2017, 06:37:34 pm
content: Quote from: T3sl4co1l on November 16, 2017, 09:42:59 amWhat is this a chip?Sent from my iPhone using Tapatalk

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: November 20, 2017, 06:43:51 pm
content: I guess we are all asking what exactly your circuit does, and why you need it to cut off at a certain voltage. Then we can make suggestions as to how.For instance, a battery charger circuit does not need toreact super fast and blow a fuse when the battery is charged.a comparator with a relay or solid state switch of some sort would work well.However, a power supply feeding sensitive equipment that needs protection against component failure failure (e.g. Pass transistor shorting) does need this (like a crowbar).So please elaborate on what exactly you are trying to do.

author: dclevy1
author_rank: Contributor
timestamp: November 20, 2017, 10:38:57 pm
content: Quote from: FlyingHacker on November 20, 2017, 06:43:51 pmI stated earlier I didn't remember what I needed it for since this thread is months old. But instead I wanted some scenarios on different modules or devices I could use in cause I needed to remedy this issue again.Sent from my iPhone using Tapatalk

author: cdev
author_rank: Super Contributor
timestamp: November 20, 2017, 10:42:35 pm
content: You can mount the voltage regulator on a heat sink on the exterior of the device, outside its cabinet, if the application is one where it's heat could cause problems.

author: dclevy1
author_rank: Contributor
timestamp: November 21, 2017, 12:44:52 am
content: Quote from: cdev on November 20, 2017, 10:42:35 pmWhat about something that actually cuts off the voltageSent from my iPhone using Tapatalk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 21, 2017, 04:55:08 am
content: Quote from: dclevy1 on November 21, 2017, 12:44:52 amDid you look up LTC4380? That sort of thing seems exactly what you're asking about.Other keywords that may help: under/over voltage lockout, surge protection, hot plugging, protected power switch, etc.Tim

author: dclevy1
author_rank: Contributor
timestamp: November 21, 2017, 02:25:25 pm
content: Quote from: T3sl4co1l on November 21, 2017, 04:55:08 amI'll look this up right nowSent from my iPhone using Tapatalk

author: dclevy1
author_rank: Contributor
timestamp: November 21, 2017, 02:29:05 pm
content: Quote from: T3sl4co1l on November 21, 2017, 04:55:08 amSo this is only a chip how would I implement this into a circuit I'm not that educated when it comes to breadboards.Sent from my iPhone using Tapatalk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 21, 2017, 04:16:26 pm
content: They have evaluation boards available for most chips. Not the cheapest thing, but definitely the easiest thing!Tim

author: Zero999
author_rank: Super Contributor
timestamp: November 21, 2017, 04:29:59 pm
content: Quote from: dclevy1 on November 21, 2017, 12:44:52 amThe TL431 plus a BJT and MOSFET. Some hysteresis my help improve the speed, but it's not normally necessary for stability, since disconnecting the load, tends to further increase the supply voltage, resulting in a positive feedback loop, causing it to turn off more.This sort of thing has been discussed before. Refer to the thread linked below:https://www.eevblog.com/forum/beginners/2n7000-strange-behaviour/msg1186642/#msg1186642