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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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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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Polyfuse value - laptop motherboard

Hello collective wisdom, I need to replace a surface mount Polyfuse on a laptop motherboard. However, I don't think there is a value on the fuse itself (there is what looks like a I or maybe a 1). ...
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29 views

What negative effect may a polyswitch have on Li-Po/Li-ion charging?

I have a single-cell Li-Po battery (3.7V 380mAh) connected to a dedicated charge controller (TI bq21040). The programmed charge current is 180mA. Although the battery is shipped with a PCB with ...
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3answers
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Question about 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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190 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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77 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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45 views

How effective is CID and PTC protection on batteries?

There is a source that states: 18650 batteries sold in the US are required to have CID and PTC protection. I've read that CID is just an insulation layer, and PTC is a resettable fuse which ...
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113 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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1answer
40 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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99 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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1answer
69 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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75 views

Black plastic electrical component

I took the housing off a portable AC because the plug end circuit breaker pops immediately when you try to reset it. Inside the box that houses the control board and wire junctions I found this little ...
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179 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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110 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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404 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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160 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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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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2answers
80 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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1answer
262 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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0answers
121 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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1answer
452 views

Lifepo4 current limiter with supercapacitor in parallell

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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3answers
419 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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241 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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2answers
352 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 ...
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241 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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981 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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1answer
1k 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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1answer
510 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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697 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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2answers
2k 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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1answer
1k views

Alternatives for automotive fuses?

So be I recently asked a question about using a PCB design for a fusebox (link here: PCB design for automotive fusebox?) but since recently come across two other fuse alternatives: PPTCs and ...
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2answers
3k views

Can I parallel multiple resettable fuses to achieve a higher current rating?

I have an application wherein I spec'd a fuse, rated for 80VDC 500A. The customer is concerned about what happens if they have to replace the fuse, it being rather difficult to access. They suggested ...
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2answers
2k views

Replacing glass fuse with reset button fuse?

Several months ago i made a 10Amper power supply with 5 outputs, each output has a fuse holder for crystal 10A Fuses, they work as intended but its a chore to replace them every time i short them, i ...
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3k views

Short circuit protection for high current wearable: fuse, polyswitch, TBU, circuit breaker, something else?

I am thinking about design elements for a rather high current, battery powered, wearable application. Maximum current of 40A at 5V, but typically around a third to a half of that. Power would come ...
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2answers
4k views

Polyfuse (resettable PTC) lifetime

There is a proposed design that could have a polyfuse tripping many times. Is there any lifetime to these things? Number of resets? I looked here but could find no such spec. http://www....
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886 views

Crowbar circuit OrCAD simulation

I have a couple of issues with the simulation; The zener diode has Vz at 4.7V, it is not behaving as expected since it is reducing the supply voltage by 4.7 instead of setting it to that voltage. ...
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How can PTC resettable fuses (battery strap type) be mounted on PCB?

I need to use a resettable fuse in my design and I'm using something like this: Can strap type fuses be used on PCB and how can they be mounted on PCB?
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1answer
204 views

Does USB require protection if it is only connected to the regulator input?

I have the following schematic powering my circuit. Is it required that I protect the USB power pin with some fuse?
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1answer
2k views

Options for a simple over-temperature cut-off?

I am designing a heater circuit that will be used in a product to be produced in small to medium quantities (hundreds to thousands of units, not tens of thousands). This heater will be PWM controlled ...
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5answers
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Why do 0.02A fuses not protect a person? Why no protection from shocks?

I understand the user here so that fuses do not protect people from shocks. I am planning to put put fuses such as fast-blown fuses and PPTC fuses around all kind of positions such as computerUSB-...
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2answers
2k views

PTC fuse resistance characteristic?

I'm currently working on a project where I have to take into account the resistance of the in series PTC fuse, however after reading the datasheet I found two specs for resistance Rmin and R1max. I ...
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1answer
318 views

Question regarding fuses

What is the difference between thermal fuse and MOV and polyfuse.Which is faster and also which companies produce polyfuse, especially in Asia. I have to search for a component that can save my ...
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4answers
1k views

Dual AC feed to power a DC unit (Raspberry Pi) with Diode and Polyfuse for protection

I wish to place some Raspberry Pi's in remote locations (data centres) for telemetry and other services like serial OOB access. Typically dual AC feeds are presented to customers in a data centre ...
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8k views

How do I measure startup/inrush current?

I have some small devices that draw 20mA. I'd like to add a resettable (PPTC) fuse to them but I am not sure what value to select. My thought is I need to find a value that will tolerate the startup ...
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2answers
3k views

PTC Fuses and Low Current Circuit Protection

I would like to have some overcurrent protection in a circuit that normally does not draw much current (~100mA max.) I like the idea of PTC fuses, but they seem to be extremely slow in disconnecting ...
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1answer
2k views

Help designing an inverse polarity and overload (crowbar) protection circuit

There are some great resources on the internet and on this site about designing various protection (crowbar) circuits. For example, Leon's answer to a general circuit protection question. I'm looking ...
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4answers
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How do I make an opamp comparator work in schmitt-trigger mode?

I want to control a small 12V case fan. I will set values of R1, R2 and R3 so that the fan will work above temperatures 40oC. I understand that in these kind of systems, there will be an indecisive ...
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Why do PTC fuses have different voltage ratings depending on package size / hold current?

I've been trying to figure out the PTC fuse I want to use in a little automotive power supply circuit and I'm a little disconcerted by the max Vdc ratings most of these things have. For instance, ...
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4answers
13k views

How do I choose a fuse? Fusible Links vs Polyfuse?

I realise this is an extremely broad subject area but I need to know how to choose a fuse to protect a circuit. Recently, a cheap PSU of a friend's blew up quite spectacularly (the two primary ...
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3answers
2k views

How to use a Polyswitch Self Resetting Fuse and light up led when fuse has been disconnected

I'm designing a circuit that will be connected to usb of a pc. How can I isolate the supply when a short has been detected on any part of the circuit. An led should light up indicating there's a short ...