Resettable fuse, the operating principle, device and application
Hello dear readers! Today I want to talk to you about this exciting Radioelement as a resettable fuse (SP), will talk about the strengths and weaknesses of its sides, and I will say a few words about their application.
Content
The device and principle of operation
The main parameters of the joint venture
Pros and cons of Resettable Fuses
Application area
The device and principle of operation
So, first let's find out what principle operates our resettable fuse, and what's inside. Original name Resettable Fuses - PolySwitch. it PPTC (Polymeric Positive Temperature Coefficient) - the product with a positive temperature coefficient of resistance.
Externally, the SP is a circular or square plate with a pin, if the product is intended for mounting on TNT technology. A may also have the form of rectangular plates (such as resistance) if they are intended for SMT mounting.
So in essence the joint venture is much closer to the thermistor or bimetal thermal cut than to the usual fuse.
Home SP chip lies in the fact that it is based, a special Toko nonconductive polymer matrix in which is embedded a conductive carbon forming conductive paths.
And while the track flowing rated current, nothing happens through the generation of carbon. But as soon as its value increases above a certain limit, the polymeric material starts to heat up, and at some point in time navigates polymer in the amorphous state. As a result, the product increases in size and starts the process of breaking conductive traces of graphite.
This entails an increase in resistance, which leads to further heat the fuse. This leads to an increased resistance which greatly completely stops the flow of current through the circuit, thus protecting the device.
Once the appliance has cooled, the polymer starts reverse process of crystallization and recovery of the conducting paths, i.e. the fuse again begins to conduct current.
The temperature dependence of the resistance is as follows
The figure above shows that as the temperature self-healing fuse is located between the points 1-2, The product is energized. Upon reaching a certain temperature level and the resistance starts to increase already in the interval 3-4 varies exponentially.
The main parameters of the joint venture
1. Umax (B) - the maximum voltage that can withstand the product and does not collapse.
2. Lh (A) - nominal current, which is able to pass through without triggering the SP itself.
3. Itrip (A) - The minimum current at which triggered resettable fuse.
4. rmin; R1max. One of the most important parameters Rmin shows resistance to the product prior to the first actuation. R1max - the resistance fuse one hour after the operation. These parameters are always specified for a specific ambient temperature.
The smaller of these parameters, the better. Because SP is switched in series and if it will have a sufficiently high resistance, then it will dissipate power of the appliance, which is undesirable.
5. Operating temperature and activation temperature. Working temperature range is called in which a minimum resistance and resistance after tripping almost invariably this corridor varies from -40 to +85 degrees Celsius. A trigger temperature is typically 125 degrees Celsius.
6. Imax - the maximum short-circuit current, which maintains the product without breaking.
7. response speed Max. Time to Trip - this is the time during which the superconducting transition from the working state to the load. It is also a very important parameter, and then running the rule: the less the better.
And now let's move on to the pros and cons of the product.
Pros and cons of Resettable Fuses
So, of the benefits you can highlight the fact that in the case of activation of this product should not be changed, such as a conventional fuse.
But cons him a bit more:
Sufficiently low response time. We have made clear to start the process in the polymeric material, it is necessary to warm up and it turns out that such protection switching speed is relatively slow and depends on the initial temperature JV.
That is, if the equipment is used in a wide temperature range, for its protection applies JV undesirable.
As there is still one significant disadvantage, even after the first operation of the product can not be restored to the original parameters.
And it turns out that just a couple of three positives product needs to be changed because it is not properly carry out its protective function. And this should be one more conclusion that the products, which are frequent overload, such protective elements are undesirable for use.
Application area
Despite some serious shortcomings, such protective elements are widely used, for example, in the pulse flanks Food, but not as a separate protection element, in the complex, together with other much more quick protective devices.
That's all I wanted to tell you about a resettable fuse. If you liked this article, then vote her huskies and thank you very much for your attention!