Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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.

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.

Ployfuses have different applications, and design issues, from fusible links.

Questions about regular fuses (fusible links) should use the tag.

Please keep in mind that repair questions are typically closed if not within the scope of the Site and FAQ.

77 questions
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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 MOSFETs blew up - dead shorts.) It claimed 400W but on…
Thomas O
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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. I'm a little worried by the design... but perhaps needlessly. I'll send…
George Herold
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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 topic: The keyboard or mouse should not draw more…
drudru
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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 power from these types of circuits. Why do PTC…
DOS
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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 did a little more research and I came across this…
Kvegaoro
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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 used a polyfuse since I don't want to have to…
Colin
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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 short circuit at the load side. The problem is…
syoma
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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 region in which the comparator output will be fast…
hkBattousai
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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 that side of the fuse that is opposite to the energy…
tobalt
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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 from RC car battery packs through a DC-DC converter.…
Robert Atkins
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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 or inrush current when the circuit first turned…
JYelton
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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 supercapacitors do the heavy lifting, I need to limit…
skogs
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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 resettable fuses as an option. I'm not aware of…
Stephen Collings
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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 (non-ganged) be protected by a polyfuse with hold…
user21820
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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). So I'm fine with 4A max input current. I'm trying…
Sandro
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