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 ...

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1answer
53 views

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?
2
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1answer
106 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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0answers
82 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
469 views

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 ...
3
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1answer
148 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 ...
3
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1answer
114 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
391 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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3answers
2k 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
674 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
662 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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3answers
2k views

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 ...
3
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2answers
1k views

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
5k 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
686 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 ...
3
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3answers
269 views

Are PTC fuses called some other way?

I recently learnt about the existence of PTC fuses, and I'd like to use one for an USB power supply I'm building. I guess there are PTC fuses on the PC side, but you never know. I went happily to buy ...
3
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2answers
234 views

Are PTC/resettable fuses really moisture senstive?

I recently bought some 0805 Multicomp PTC/resettable fuses from Farnell. They were MC36213 (500mA) and MC36206 (200mA). I plan to use these in product which may exist in a high humidity (~80-90%) ...
3
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3answers
477 views

Why are polyfuses so big?

Why are polyfuses so big? I was looking at a 500mA polyfuse, it is in an 0805 package, but there was only one of them - the rest were 1206. I have two questions. Why so big? Does anyone make 0603 ...