Circuit protection - Page 1
Forum section: electronics / beginners

author: Jr.Maxwell
author_rank: Contributor
timestamp: March 16, 2020, 08:35:28 am
content: Hello Community,I'm designing a circuit and came across a challenge. I want to create a fault protection circuit but can seem to figure out in what order to place my sub fault protection circuit on the board.So as of now, I'm sure that I need th following: Reverse voltage polarity, ESD, fuse, over voltage protection and high frequency filter. - see Attachment -- But I stil can't figure out how to order them in the circuit, what goes first? where can I learn more about this?Best regards,Maxwell

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: March 16, 2020, 09:11:20 am
content: High-frequency noise filter is active or passive?

author: Jr.Maxwell
author_rank: Contributor
timestamp: March 16, 2020, 09:18:33 am
content: passive:)

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: March 16, 2020, 09:26:26 am
content: So my suggestion is only moving the overvoltage protection before the rest of the circuit because the rest of the circuit consumes current and causes a voltage drop, so for proper voltage protection move this stage there.if the difference between the circuit voltage and over-voltage threshold is high, it doesn't matter, the current draw is okay.

author: Jr.Maxwell
author_rank: Contributor
timestamp: March 16, 2020, 12:29:30 pm
content: So even before the fuse? Wouldn't the fuse help protect the over voltage protection? I can replace a blown fuse but not integral parts on the PCB

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: March 16, 2020, 01:56:03 pm
content: Quote from: Jr.Maxwell on March 16, 2020, 12:29:30 pmNo, in that condition you gonna put the over voltage protection stage before circuit and after the filter. otherwise, the current state is okay. Fuse does not protect against over voltage. just over current.

author: Jr.Maxwell
author_rank: Contributor
timestamp: March 16, 2020, 08:36:19 pm
content: Ah I understand thanks! This was really helpfulI still have 1 question though, Why would I put the filter BEFORE the over voltage protection? why is it better to directly filter before even protecting?

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: March 16, 2020, 09:20:13 pm
content: Quote from: Jr.Maxwell on March 16, 2020, 08:36:19 pmI told you why, if the load consumes high current and your voltage protection is tight, for example, the circuit consumes 9V and voltage protection is 12V, then this might cause misbehavior. otherwise, if the protection voltage is much higher than the circuit input voltage, it doesn't matter, you can install it at the input.The filter is passive and it introduces a drop in the first case.

author: hsn93
author_rank: Regular Contributor
timestamp: March 17, 2020, 06:01:08 am
content: Quote from: hesam.moshiri on March 16, 2020, 09:26:26 amim not experienced enough to say this but if over voltage fail short you get UL safety problems there right?

author: not1xor1
author_rank: Frequent Contributor
timestamp: March 17, 2020, 06:32:04 am
content: Quote from: hesam.moshiri on March 16, 2020, 01:56:03 pmA fuse is an essential part of a shunt type overvoltage protection, like that shown in the block schematic.Overvoltage protection is usually achieved by a circuit that sinks a negligible current when voltage is below a given threshold and behaves like a sort of short when the voltage gets above the threshold and so needs a fuse to open the circuit as it can withstand a large amount of current just for a very short time.Such devices may make use of gas discharge tubes, MOVs, TVS or zener diodes, crowbar circuits and so on.A TVS diode may work both as overvoltage and reverse polarity protection if a low voltage reverse polarity is unlikely to damage the protected circuit.

author: hesam.moshiri
author_rank: Regular Contributor
timestamp: March 17, 2020, 08:39:24 am
content: Quote from: not1xor1 on March 17, 2020, 06:32:04 amNO, because as you said USUALLY and generally. before the fuse blows and cuts the path, the circuit is already dead. we don't know what is the connected circuit. we don't know what is the overvoltage condition. the overvoltage could be a few volts more than an absolute maximum of a component such as an Opamp and kills it. we don't know. when such a circuit starts to draw much current, it is already dead.