Questions tagged [polyfuse]

Questions regarding Polymeric Positive Temperature Coefficient devices, typically known as Polyfuses, PPTC, or Resettable Fuse. They are non-self-destructing versions of Fuses, similar to Circuit Breakers, in that they self reset when the high current draw is removed. Questions about regular fuses should use the Fuse tag.

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\$ I^{2}t \$ calculation issue

I tried to select the fuse based on this selection guide, but found my calculation for fuse I2t is not practical. Can someone point out the error in my calculation? The application scenario is a 240V ...
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2 votes
3 answers
106 views

Polyfuse voltage significance

I would like to protect a circuit from overcurrent over 500 mA. The voltage in the circuit is only 5 V. Can I use higher voltage and lower current polyfuse, which results in same power flowing through ...
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4 votes
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Self resetting crowbar circuit for over voltage protection

I'm trying to design an over voltage protection circuit that doesn't rely on custom chips (the chip shortage has shown the danger of relying on this,) so I put together a crowbar circuit like this: I ...
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8 votes
9 answers
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Do I misunderstand fuses?

A statement that I often read here goes: "Fuses protect the wire, not the load." However, in basically all cases I use fuses, I think they are there to protect the load - I.e. the device on ...
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3 votes
1 answer
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PTC fuse failure mode?

PTC fuses are resettable, i.e. they go to high resistance when tripped and return to low resistance when they cool. Some examples would be e.g. Bel fuse 0ZCJ or Littelfuse Polyfuse series. One thing ...
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PTC Resettable fuse

I need to limit the current of a motor to around 1A. I would like to use a PTC fuse so that it trips in the rare occasion the motor is forced by the user to draw too much current because the motor is ...
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1 answer
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Polyfuse for AC line no 10A? [closed]

I have a circuit where I would like to replace standard 10A glass fuses with some resettable solution. I have looked into polyfuses: https://lcsc.com/products/PTC-Resettable-Fuses_11042.html?q=poly%...
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0 votes
1 answer
251 views

Protection circuit with polyfuse and zener

I'm designing a protection circuit with polyfuse and zener for DC 5v input. I have try it fisically but the polyfuse never trigger because the zener burns before when I plug 6-12V to the input. My ...
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11 votes
3 answers
3k views

What would it take to make a PS/2 keyboard interface hot-swap?

A long time ago, I had to service some of the early Compaq Desktop PCs. They used to have fuses on the motherboard that blew when a customer hot-plugged a keyboard. I found this when googling on the ...
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141 views

Circuit protection with TVS and polyfuse

I have a 36V system that has to be protected against 1000V surges as described by IEC61000-4-5. Some SMC TVS diodes are rated for this exact purpose and are able to conduct the surge pulses without ...
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1 vote
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What are the determining factors for using a polyfuse in electronics circuit design?

When designing electronic circuits (PCBs) I often wonder if I should use a polyfuse (aka polyswitch, PPTC, PTC resettable fuse) at the power inputs and outputs or not. So basically what I am asking ...
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1 vote
2 answers
152 views

Digital input protection circuit [closed]

Can anyone explain to me how this circuit works? I am familiar with the traditional Zener diode as voltage regulator (with a resistor,) but I couldn't tell what the fuse does here and why the 10K ...
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270 views

Choosing fuse for 2S li-po

I Have 2S 8000 mAh li-po battery I want to use as an external power source for my DSLR camera (Canon 7D Mark II). Previously, I failed to power it with power bank and DC-DC converter, most probably ...
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0 votes
1 answer
254 views

How to identify the polyfuse used in this RS-485 module

This is the popular RS-485 module found in the market, how can I identify the polyfuse/heat recovery fuse in it? Also its manufacturer or electrical ratings?
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What PolyFuse should I have to protect 150 Ohms 0.5W resistor?

I need help selecting a polyfuse for protecting a 150 Ohms 0.5W resistor. My goals are: To make sure that the resistor won't take any damage when I apply voltage over 3V onto the 150 Ohm resistor I ...
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6 votes
5 answers
3k views

What polyfuses protect USB ports in a typical modern PC?

I would like to know what is the typical rating of a polyfuse used on modern PCs (desktop or laptop) with USB 2.0 and 3.0. TE Connectivity apparently recommended in 2011 that a single USB 2.0 port (...
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1 vote
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Protect a PTC from being touched

I am considering using PTC to protect PS/2 keyboard +5V power line. As it is low probability that there's something wrong will be inserted into the 6-pin mini-DIN connector, IMHO it is not necessary ...
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How to wire a PPTC polyswitch + blown indicator LED to protect a bi-directional DC motor from stalling?

I have the following setup and it works well as is, except that I would like to protect the 12V DC motors (Reverse High Torque Permanent Magnet 12V DC motor) with a PPTC polyswitch + a LED to indicate ...
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1 vote
2 answers
286 views

Why is voltage specification irrelevant in tripping a PPTC polyswitch?

In a circuit, a resettable fuse (or polyswitch or PPTC) is a kind of breaker component that trips when the AMPERAGE exceeds a given treshold to protect against overcurrent faults. PPTC basically ...
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0 votes
2 answers
366 views

Selection of resettable fuse (PTC) for the board

I am create a board that will have: MCU Atmega328P - x1 SK6812 RGBW LED - x9 The maximum current according to my calculations is 650mA (at full brightness of all LEDs, taking into account the margin)...
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1 answer
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Deliberating shorting PTC to toggle between FBR and HBR

We're designing a board that needs to interface with a variety of different furnace control boards, some of which have full-bridge rectifiers and some of which have half-bridge rectifiers. Depending ...
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1 vote
1 answer
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PTCs on AC/mains line

Why is it that surface mount (SMT) PTC fuses can only be used on DC lines but through-hole PTC fuses can be used for both AC and DC? This came from a cautionary note on one of Bel Fuse's PTC ...
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1 vote
2 answers
538 views

Why less protection on a GPIO RS485 board compared to an UART RS485 board?

When I search for RS485 board (to be used for my Arduino to control DMX512), I find mostly two types: GPIO / TTL based (which I want to use), like TTL RS485, which mainly has a MAX485 and some ...
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5 votes
3 answers
979 views

Polyfuse with Crowbar for Over Voltage

I am looking to add overvoltage protection to a circuit of mine. A standard way of doing this is with a crowbar circuit with a fuse to blow when tripped, thus disconnecting the circuit. However, I ...
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1 vote
1 answer
349 views

Will my zener diode work again with a polyfuse after a overvoltage?

I am trying to make a simple overvoltage & current limiting circuit for my PCB. I made the following circuit. The zener will break down and conduct current to ground. Since its resistance has ...
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0 votes
3 answers
117 views

Straightening the pins of a resettable polyfuse

I have resettable polyfuses like the picture below. I am working on some PCB boards where I solder the wires myself on the PCB. Because it is very hard/cumbersome work to solder very small wires, I ...
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0 votes
3 answers
507 views

Can a resettable thermal fuse be soldered?

Earlier related questions: How to solder a 70 °C (158 °F) thermofuse Using a thermal fuse in a PCB terminal block? History: I 'normally' soldered a nonresettable thermal fuse, which (of course) ...
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0 votes
2 answers
498 views

In a DC circuit, are there any reasons for wiring overcurrent protection such as fuse or pptc PHYSICALLY near the load?

In a DC circuit, are there any reasons for wiring overcurrent protection such as fuse, pptc, etc.... PHYSICALLY near the load(or inside it)? By wiring "physically near", I mean in the power wire going ...
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2 votes
1 answer
882 views

Exceeding Vmax rating of PTC Fuse

I am adding over-voltage, over-current protection in my circuit. My circuit/PCB has many DC-DC converters and these converters ...
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0 votes
1 answer
173 views

Connecting a polyfuse (PTC / resettable fuse) without soldering

I want to connect up a polyfuse to protect a potentially flammable USB cable and a Raspberry Pi Zero in the circuit below. However it seems that most Polyfuses are supposed to be soldered and I'd much ...
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1 vote
2 answers
334 views

Precision resettable fuses

I am a scientist, and I have found myself needing to interface two disparate pieces of equipment. I have a precise, automatically controlled current source that I wish to interface to a very ...
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1 vote
1 answer
1k views

What does it mean to trip in PTC Fuses?

Hi I want a current flowing 1A. I don't understand what does it mean to trip? (Image source - Farnell PTC datasheet) Does it mean to open the circuit? Should I be looking at a holding current that ...
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0 votes
2 answers
744 views

PPTC Resettable Fuse

I recently bought a few types of resettable fuses, but now I'm a little bit confused using them. I have bought: 30-UF200 (Hold: 2A, Trip: 4A) RUEF300 (Hold: 3A, Trip: 6A) R30400 (Hold: 4A, Trip: ...
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0 votes
1 answer
192 views

unnecessary usb protection?

I have a device with two voltage sources and therefore I need atleast a diode on the lowest source to secure it. The lowest source is a 5V USB, and it is protected with a schottky diode with a 0.5V ...
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3 votes
4 answers
1k views

Specifications to consider when selecting a polyfuse

I am designing a power supply for a flight controller, and I am finished with the regulating and almost everything else. I want to have a polyfuse on both of my inputs, but I don't know how to pick ...
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0 votes
2 answers
308 views

Non-resettable zener/polyfuse for overvoltage protection

My setup is two DC-DC converters (hobby BECs) supplies, one acting as a backup for the other. A relay, powered by the primary BEC will automatically switch to the secondary BEC if the output from the ...
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9 votes
6 answers
8k views

Simplest, cheapest, fast and minimum footprint current limiting circuit with low resistance in normal state

I have a digital output, driven by the high-side driver with nominal voltage of 24V DC. The load current normally is below 100 mA. The output is monitored, so I can switch it off quickly if I detect a ...
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0 votes
2 answers
132 views

Replacing the fast tube fuse with polymer fuse

I have a simple digital multimeter in which a fast tube fuse, rated at 0.1A and 250V is soldered directly to the plate. Now, recently this fuse blowed and I have to replace it. Because I don't want ...
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2 votes
1 answer
523 views

Extending a PTC voltage rating with series resistance

PTCs come with a maximum voltage rating which, according to the answer for this question is essentially because of instantaneous power across the device. Usually, a PTC is placed across a low-...
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2 votes
0 answers
152 views

Features of Resettable Fuses

I want to use a resettable fuse for overcurrent protection. I am a bit confused about their features. The hold current is the maximum current for not tripping and the trip current is the mimimum ...
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7 votes
2 answers
1k views

LiFePo4 current limiter with supercapacitor in parallel

I am making a LiFePo4/supercapacitor-hybrid. Spike current draw can reach 300A for a few seconds. The LiFePo4 batteries I am using is rated for 100A max discharge rate. In order to make sure the ...
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2 votes
3 answers
1k views

Fuse dimensioning guidelines

I’m looking for advice on how close to nominal current draw a fuse should be dimensioned. On the internet I have seen numbers from 125% and to 800% in different applications, which is a rather wide ...
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0 votes
0 answers
538 views

Circuit protection incorporating a Transient Voltage Supressor and Polyfuse

I want to protect some microprocessor equipment ( 5.0v, max 700mA ) which is powered by usb cell phone type chargers from damage due to such things as polarity reversal, over-voltage, power surges etc....
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2 votes
2 answers
830 views

Polyfuses in parallel for shorter trip time?

I'm thinking about protecting a 12V/20W transformer with a polyfuse. Quote from the Littlefuse datasheet: I_Hold = Hold current: maximum current device will pass without tripping in 20°C still air. ...
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0 votes
0 answers
404 views

Resettable fuse failure

I have a 1.1A, 33V resettable fuse in SMD 1812 package. To test it, I connected a 6A 20V source across it. It went up in a flame that lasted a few seconds. Should I conclude that the fuse is out of ...
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3 votes
1 answer
2k 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 ...
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3 votes
1 answer
2k views

Using Fuses to Connect Batteries in Series

I would like to create this battery pack, consisting of 13 Samsung ICR18650-26F connected in series. There are balancing leads for balanced charging, and resettable polyfuses connecting all of the ...
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  • 195
0 votes
1 answer
907 views

Can I put a zener diode *before* PTC to protect the supply?

I'm designing a small module that takes power from USB and provides it to a breadboard for prototyping. My target audience will just be hobbyists so I want to include some protection. I'm more ...
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1 vote
0 answers
1k views

PTC Reset switch Voltage drop

This question might fly close to the rule about asking to select parts. What I'm really asking is what parameters of a PTC Fuse I should be looking for. Or even should I be using one. [Software head, ...
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0 votes
2 answers
4k views

How to fuse batteries connected in series?

Is it possible to wire each battery in a series to the next using a fuse wire, so that the individual batterie's max power output is not exceeded? here is an illustration, suppose each battery had a ...
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