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Questions tagged [circuit-protection]

A device, components, or safety measure designed to protect circuits from overvoltage, overcurrent, a combination of these; or the theory of same.

18
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10answers
7k views

AC: Why differentiate between Ground and Neutral?

Current flows through a conductor connecting points at different potentials. Leaving aside multi-phase details, common/conventional AC systems use a 3-wire setup: Wire-1: a line/live/hot/phase wire ...
15
votes
5answers
11k views

Why (not) put a resistor on FET gate?

While thinking of ways to protect a MOSFET one idea was to put an extremely high resistance in front of the gate: The idea being that current is never supposed to flow through the gate, so if some ...
11
votes
5answers
2k views

Protecting a laptop from USB connected devices

In the past couple of months I've managed to destroy 2 perfectly good laptops through programming development electronics through USB. I've been wondering what could be done to prevent this. A couple ...
10
votes
2answers
807 views

For mains attached circuits: what do I need to protect against and how do I do it?

I don't have a lot of experience with mains voltage and designing protection circuits for them. I'm not sure: A) What do I need to protect against? I know I don't need to worry about 10kV voltage ...
10
votes
2answers
7k views

What is the recommended way to protect a circuit from non-transient overvoltage?

I'm designing a 12V battery-operated portable lighting controller, and frequently am asked about improving the run time. The simplest way is to add a second battery in parallel, but I often worry that ...
9
votes
5answers
3k views

Why aren't starter circuits protected?

In most cars and trucks, a thick cable connects the battery directly to the starter (solenoid). Why don't these circuits have have any kind of overcurrent protection? It is an accepted practice ...
7
votes
4answers
4k views

Super glue as solder mask?

Wondering if super glue could be safely used on a PCB to cover exposed traces or jumper wires. I know it’s non conductive but is there any type of damage that could occur? I normally use green ...
7
votes
4answers
3k views

Interfacing a button to a microcontroller (and PC) with a 50 m long cable

I am designing a board that will be plugged into a computer and will read the status of a button ~50 m away in an office environment (it's actually a lot closer, but the cable is long). I think ...
7
votes
2answers
461 views

What is purpose of components in this circuit

I'm trying to understand this circuit but I can't understand purpose of R4 and R6. Can someone explain their purpose?
7
votes
3answers
852 views

How can I protect veroboard from corrosion/ tarnishing?

All of my veroboard-copper-tracks gradually slowly becoming blackish, scratch-like marks, or sometimes brown-black patches. Here's one from extreme (sorry for bad soldering, it is 7- 8 months old, ...
6
votes
3answers
876 views

Fuse 125V/4A can be replaced with 250V/4A?

I want to replace a blowed fuse 125V/4A but it is rare to find them. Can I use instead a 250V/4A ? I read at https://www.mojotone.com/support/Knowledge-Base/Is-it-ok-to-replace-125v-glass-fuses-with-...
6
votes
2answers
2k views

How to limit current precisely?

I would like a way to limit the current of a circuit to exactly 100mA (+/- 2-5%). This is on a relatively high voltage circuit (100V to ground), and the current is normally pulsed with pretty fast ...
6
votes
1answer
2k views

TP4056 module parallel output

this is my first time asked on stack exchange, please bear bare with me. Anyway, I created portable monitor using multiple TP4056 as battery charger & protection circuit. But I'm not sure it's ...
5
votes
5answers
3k views

What is the metallic coating on these stranded copper wires?

The 5-colored wires's strands looks like aluminium, but it is basically copper wire at centre, with a thin conductive coating (my teacher shown it to me) of silvery-color, so that the copper doesn't ...
5
votes
2answers
658 views

Diode Clamp failing with LDO Circuit

I'm back with yet another mystery. Summary question: Why would an input to a voltage clamped circuit de-stabilize and or elevate that voltage clamp's upper rail? How do you properly clamp voltage ...
5
votes
1answer
565 views

Over voltage and reverse voltage protection of multiplexed ADC with voltage follower

I am designing a protection circuit for the ADC section of a design I am working on. There will be 8 analog signals being read by a single pin of the MCU via an 8 channel multiplexer. The analog ...
5
votes
1answer
901 views

Possible wrong use of TVS diodes?

I've been facing a weird situation and unable to find the reason behind so far, therefore I frustratedly turned up for help. I have a system comprised of 2 separated PCBs (A control box and an on-...
5
votes
2answers
9k views

How can I use two TP4056 with two li-ion batteries, but single load?

I have two TP4056 modules (with protection circuit), which I am using to charge two batteries respectively, off a single power line. The modules are the ones that have charge output (B+/B-), and ...
5
votes
2answers
124 views

±12V protection for MIDI output

TLDR; how to make a MIDI output withstand shorting it to \$\pm12\$V? I'm designing a MIDI output in a eurorack modular synth module on a TRS jack (this is a semi-standard non-standard way to save ...
5
votes
2answers
2k views

Limiting torque on a DC motor

I'm developing a small knob that can be controlled by both the user and a microcontroller. My current design is a modified servo. I'm removing most of the gearing to keep the motor's torque low. I'm ...
4
votes
2answers
1k views

Bridge Rectifier Attached to DC input

I was taking apart an old game-show buzzer system (like something they might use on Jeopardy) and I was confused by the a particular section of the circuit board: I'm pretty sure the circular ...
4
votes
3answers
3k views

Circuit breaker vs fuse timing

Recently I powered on an electrical device that was (unbeknownst to me) quite defective. It tripped the circuit breaker almost immediately (after shooting off some sparks). There was a small (600W) ...
4
votes
2answers
1k views

ECG circuit Pre amplifier

I am in the process of designing an ECG circuit to detect heartbeat abnormalities. I have two question regarding the AD8220 datasheet: What is the function of the 2.2pF, 10pF capacitor, 10k, 15k ...
4
votes
2answers
56 views

±12V protection for MIDI input

TLDR; how to make a MIDI input withstand shorting to \$\pm12V\$? This is a counterpart to this question, I'm asking this as I was inspired by the great answer I got there. I'm designing a MIDI input ...
4
votes
2answers
1k views

What factors play into choosing type of MCB (Circuit Breaker) which is B16 vs C16 vs D16?

Found these discussions and Q&As online around this and am trying to determine how/ when one would decide to choose which way to go? http://www.theiet.org/forums/forum/messageview.cfm?catid=205&...
4
votes
4answers
368 views

Is this protection circuit designed properly?

I designed this protection circuit to avoid reverse polarity and over-voltage. Here is the circuit: simulate this circuit – Schematic created using CircuitLab Is the circuit designed ...
4
votes
3answers
677 views

Does an overvoltage TVS for USB hot-plugging connect to shield ground?

I am designing a keyboard which will connect to the computer via usb-miniB to charge a LiPo battery. The datasheet for the charging IC I am using specifies overvoltage protection on the USB power ...
4
votes
2answers
4k views

1-Wire DS2480B overvoltage and ESD protection

I'm designing a series of 1-Wire components for my SmartHome Bus and use the DS2480B as Busmaster. Because the cable I run around the house has 3 wires (24V, 1-Wire, GND), I'd like to protect the ...
4
votes
1answer
287 views

Opto-coupled EIA-422 receiver (understanding suggested circuits)

I am looking at a standard for communication of marine electronics (NMEA). The standard is electrically essentially EIA-422 but it prescribes opto-coupled differential receiver pins without connection ...
3
votes
1answer
921 views

What component is represented by reference designator GT?

I can see that G represents a generator/oscillator, and T represents a Transformer, but what does GT represent?
3
votes
4answers
879 views

Short life of LED parallel to Solenoid as indicator

I have a relatively simple circuit: 12 V to a switch; on the other side of the switch is a solenoid and an LED in parallel. Nothing special about either component; the LED is a 20 mA typical LED rated ...
3
votes
2answers
2k views

Will this circuit protect my digital IOs from overvoltage conditions?

I have come up with the following circuit to protect my device's IOs from overvoltage conditions. simulate this circuit – Schematic created using CircuitLab The idea is that as soon as the ...
3
votes
1answer
2k views

Fuse current rating and breaking capacity

I want to use the following fuse to safely interrupt a buck power supply with rated parameters Input (1A, 24V)==> Output (250mA, 12V). In the datasheet of the fuse, the constructor specifies the ...
3
votes
2answers
10k views

Determine if two outlets are on the same circuit without breaker access [closed]

I live in an apartment and do not have access to the circuit breaker panel. In the summer I run two AC units, and have inadvertently tripped the breaker before while running my vacuum cleaner. This ...
3
votes
3answers
5k views

Will a RCBO 4P trip in case of neutral fault/failure/interrupt/float?

We have 3 phase power supply in my home which is used to power single phase 240V 50 hz appliances with common neutral. (Diagram in the link at the bottom) The only protection we have as of now are ...
3
votes
2answers
3k views

How to protect a P-channel MOSFET when driving a motor?

I want to switch a 12 V DC automotive fuel pump in a bench test rig using a P-channel MOSFET, as follows: simulate this circuit – Schematic created using CircuitLab This is a simple on/off ...
3
votes
3answers
116 views

How to protect againt surges if working and maximum voltage are too close

I have a circuit that I want to protect against surges and eventual peaks (e.g. indirect lightning surges) and I was thinking about TVS diodes or MOV. The situation is: -My circuit input is 48V that ...
3
votes
3answers
383 views

Over-current-protecting a single-ended solid-state switch

A previous circuit used a ULN2003 Darlington pair as a single-ended (N-side) solid-state switch with a maximum current capacity of about 500mA. http://www.st.com/resource/en/datasheet/uln2001.pdf ...
3
votes
2answers
343 views

Bridge rectifier - min. required protective resistor

Looking at the datasheet for a MYS80 bridge rectifier, at the bottom it states Min. required protective resistor is 8 ohm. I could not find much information about a protective resistor in regard to ...
3
votes
3answers
3k views

Short circuit protection of cable

I know cables are protected from short-circuit by using fuses / circuit breakers. Cables have I²t curves, which should be checked with fuses or cb's I²t curves in time / current chart. Here I have ...
3
votes
3answers
481 views

Device shutdown: harm from charged capacitors?

In my application, I have 220nF capacitors connected to the inputs of an A/D converter (MCP3204). Now I wonder what will happen when the circuit shuts down and the supply voltage drops below the ...
3
votes
1answer
2k views

Overvoltage protection for RS485 inputs

I am using an Analog Devices ADM483E RS485-chip to build a device with RS485-capability. Datasheet here: http://www.analog.com/media/en/technical-documentation/data-sheets/ADM483E.pdf . The finished ...
3
votes
3answers
236 views

History of ESD protection

These days you can't read anything about electronics without hearing about the dire consequences of omitting ESD protection from your designs. It seems this wasn't always the case. If you look at ...
3
votes
3answers
3k views

Designing Under/Over Voltage LiPo protection circuit

I am currently trying to design a protection circuit for a project of mine that uses a single cell 3.7v lithium ion battery. I found this image online which uses 2 TL431s: However, I am really not ...
3
votes
2answers
110 views

Power supply and circuit breaker for a bursty device

I have a device (a strobe light) which draws up to 15 A for up to 50 ms at a time, but doesn't allow duty cycles over 0.1. This means that the average current is at most 1.5 A. For instance, if you ...
3
votes
1answer
389 views

I'm looking for help designing a circuit that lights LEDs in response to physical output on a small electric generator

I made a little display for kids that various non-profits have been using that helps them understand how much electricity different kinds of lightbulbs use. It's very simple, using bike parts to ...
3
votes
1answer
1k views

24V Circuit Protection - Fuse, TVS Diode, RC Snubber

I have pored over data sheets and read numerous articles on circuit protection. I understand conceptually, but I don’t trust my level of knowledge to implement it optimally. I want to be as specific ...
3
votes
1answer
332 views

Bypassing a polarity protection diode with a part of a circuit. Dangerous?

I recently built a logic probe adapting a circuit from an old magazine. One of the modifications I introduced is adding a polarity protection diode (1N4007) in series with the positive power rail, ...
3
votes
2answers
1k views

How to control over-voltage at high voltage?

Suppose we're using a voltage multiplier to charge a high-voltage capacitor (C Big in the diagram). If you significantly exceed the capacitor's voltage you'll ...
3
votes
1answer
126 views

Sprinkle switching circuits liberally with small capacitors?

I have now read enough applied circuit diagrams that I believe I'm missing something that is obvious to those skilled in the art: Where an abstract diagram has a few components, a complete wiring ...