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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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1 Cell LFP Battery Pack Protection

I am starting a project that requires a single 3.2V LiFePO4 18650 cell to be in a housing with exposed contacts, suitable for easy swapping in and out of an unpowered device. The device will only be ...
zambetti's user avatar
3 votes
6 answers
778 views

Is there a better way to protect my power supply other than the efuse?

I use fairly cheap standard power supplies with no protection in my circuit experiments, usually with output of 5V, 12V, 18V, 30V and a current up to 1A. I use standard glass fuses to protect these ...
Shamooooot's user avatar
0 votes
0 answers
47 views

SMD PTC Fuse for 24 VDC

I am designing a new version of a PCB board with a microcontroller to drive two 24 V DC brushed motors, and I am looking for a self-resetting PTC SMD fuse for a 24 VDC supply line and max 2.5 A. The ...
Alinik's user avatar
  • 179
5 votes
1 answer
433 views

Overcurrent protection (at 4A 100V)

On the PCB I'm designing, the total power consumption might be as high as 86W (including output power), with supply voltage between 18 and 75V DC (it is OK not to allow full output power bellow 22V). ...
Sandro's user avatar
  • 7,572
0 votes
1 answer
748 views

How to use TVS diode for Overvoltage Protection while powering Arduino on Vin Pin?

I am trying to make a protection circuit for Arduino nano to protecting overvoltage. Normally if I powering "Clone" arduino NANO with 12 Volt, Arduino nano is starting to smoke. So I've ...
mehmet's user avatar
  • 1,139
0 votes
2 answers
439 views

Why don't Arduinos have a fuse on the Vin pin?

I am designing a PCB for an Arduino Nano. I want to protect the Nano from over current and high voltage. In the schematic of the Nano, there is only one fuse at USB Vcc at Arduino Nano Rev3. No clone ...
mehmet's user avatar
  • 1,139
1 vote
0 answers
595 views

\$ 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 ...
Ross's user avatar
  • 570
2 votes
3 answers
493 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 ...
zmechanic's user avatar
  • 304
9 votes
2 answers
2k views

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 ...
Colin's user avatar
  • 345
8 votes
9 answers
4k views

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 ...
tobalt's user avatar
  • 22.3k
6 votes
4 answers
1k views

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 ...
Barleyman's user avatar
  • 3,656
1 vote
1 answer
633 views

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 ...
MRB's user avatar
  • 412
0 votes
1 answer
118 views

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%...
user avatar
1 vote
1 answer
913 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 ...
Santi's user avatar
  • 13
13 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 ...
drudru's user avatar
  • 241
1 vote
0 answers
393 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 ...
Arcatus's user avatar
  • 1,845
3 votes
0 answers
254 views

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 ...
CatastrophicFailure's user avatar
1 vote
2 answers
348 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 ...
PCB-ABBS's user avatar
  • 176
0 votes
1 answer
553 views

Choosing fuse for 2S Li-po

I have a 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 a power bank and a DC-DC converter, most ...
Oki's user avatar
  • 19
0 votes
1 answer
787 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?
HKP's user avatar
  • 43
0 votes
0 answers
51 views

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 ...
euraad's user avatar
  • 1,320
6 votes
5 answers
6k 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 (...
user21820's user avatar
  • 176
1 vote
0 answers
86 views

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 ...
Anonymous's user avatar
  • 7,120
0 votes
1 answer
328 views

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 ...
that-ben's user avatar
  • 363
1 vote
2 answers
450 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 ...
that-ben's user avatar
  • 363
0 votes
2 answers
478 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)...
Delta's user avatar
  • 535
0 votes
1 answer
66 views

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 ...
YNGVV's user avatar
  • 195
3 votes
1 answer
2k views

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 ...
YNGVV's user avatar
  • 195
1 vote
2 answers
1k 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 ...
Michel Keijzers's user avatar
5 votes
3 answers
1k 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 ...
Dutchmanjonny's user avatar
1 vote
1 answer
576 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 ...
Edris's user avatar
  • 13
0 votes
3 answers
153 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 ...
Michel Keijzers's user avatar
0 votes
3 answers
820 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) ...
Michel Keijzers's user avatar
0 votes
2 answers
600 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 ...
Chance-the-Gardener's user avatar
2 votes
1 answer
2k 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 ...
abhiarora's user avatar
  • 962
0 votes
1 answer
315 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 ...
Matt's user avatar
  • 185
1 vote
2 answers
487 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 ...
Landak's user avatar
  • 655
1 vote
1 answer
2k 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 ...
Nikko's user avatar
  • 145
0 votes
2 answers
1k 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: ...
beic's user avatar
  • 35
0 votes
1 answer
206 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 ...
Ole Halvor's user avatar
3 votes
4 answers
2k 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 ...
Ole Halvor's user avatar
0 votes
2 answers
332 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 ...
T Kilney's user avatar
9 votes
6 answers
11k 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 ...
syoma's user avatar
  • 191
0 votes
2 answers
192 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 ...
Pygmalion's user avatar
  • 555
2 votes
1 answer
731 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-...
Damien's user avatar
  • 1,504
2 votes
0 answers
175 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 ...
Konstantinos Tsoumanis's user avatar
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 ...
skogs's user avatar
  • 71
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 ...
NoobPointerException's user avatar
0 votes
0 answers
613 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....
6v6gt's user avatar
  • 228
2 votes
2 answers
938 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. ...
Jasper's user avatar
  • 167