How does a self-resetting fuse work?
Polymer self-resetting fuse
is a matrix of non-conducting polymer mixed with carbon black.
... After eliminating the short circuit, when the flowing current drops to its original value, the fuse
cools down and its resistance returns to its original value.
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Design
The device resembles in appearance an extension cord with a switch off button, this is partly true, but in addition to the block with sockets and wires, filter elements are also located inside. They are precisely needed to protect against power surges and filter interference.
The simplest surge protector has a varistor inside. This is a semiconductor device that, when a certain voltage is exceeded, goes into a state of breakdown. It is used in surge protectors and power supplies to protect against voltage surges. Depending on the type of varistor, it can suppress pulses of different sizes.
This version of the varistor is the cheapest, since it does not filter anything other than voltage surges. Interference continues to leak into the network and interfere with surrounding and powered equipment.
L, LC and RLC filters are widely used to filter high-frequency interference; they are also installed in network filters and power supplies.
In addition to such options, there are also models where the power cord passes through a ferrite ring, or makes a couple of turns around it. In fact, this is another L (inductive) element, which is needed to filter the high-frequency component of the spectrum.
Replacing the fuse in the surge protector
- Short circuit. Phase and zero are connected without load. This situation occurs when a wire breaks or a short circuit occurs in any device. In this case, the surge protector turns off all equipment.
- Interference. They arise due to devices connected to the network with switching power supplies. Such equipment includes computers and televisions. High-frequency interference does not damage electronics, but it does degrade its performance. Ripples appear on the screens of analogue TVs, the image is distorted, and extraneous sounds appear in the audio equipment. Extraneous signals distort the operation of sound recording and sound reproducing devices.
- Voltage surges. They can be caused by devices with inductive loads, for example, refrigerators, welding machines.
What is a filter
A surge protector for a computer, washing machine and other household appliances is a device that protects a computer and other electronic equipment from voltage surges in the power supply network.
Photo – Modern filters
Many people think that network converters and extenders have a completely insignificant difference: while an extender simply splits the output signal into several ports, a filter is designed to protect computers, TVs and other electronics from alternating voltage, as well as interference with the power line. The main difference is that the filter can withstand not only constant loads, but also sudden circuits, lightning strikes, and can even work to save personal data during sudden lights out.
Surge filter: typical diagram
With the correct assembly of any surge protector, the signal quality will noticeably increase. The device of a network extension cable is an interference suppressor, mech 4, closed with a cover made of insulating material.
The smooth change in attenuation coefficient in accordance with 14 shows that the filter is not ideal in the stopband. For example, an extension filter Fig.
It also reduces the level of network noise generated by refrigeration units when switching on and off.
It is important to ensure correct phasing of the windings. But other, less significant signal jumps may be slightly reduced due to the voltage drop across the resistors. At the same time, the operation of the power supply of a computer, monitor, audio system and other devices is pulsed in nature. From the LFC it is clearly visible how the signal is suppressed at high frequencies.
The most unpleasant thing is that the amplitude of the interference voltage can amount to hundreds, or even thousands of volts. Diagram of filter circuits for installation in an extension socket.
DIY surge protector
In Fig. It is best to mount the varistor so that it can be replaced if necessary without removing the circuit board from the housing. These filters, usually in a single-stage configuration, are housed in a compact housing and have a limited maximum capacity. Therefore, manufacturing a device that can extend or even save the life of expensive equipment is a very profitable endeavor. There are a great many outliers in the network, and they arise for various reasons.
The diagram of the simplest notch filter and the qualitative dependences for it are shown in Fig. The axes of the coils are located at an angle of 90 degrees. The frequency response of the bandpass filter has two cutoff frequencies, which are located to the left and right of the resonant frequency f0, and are also determined at a level of -3 dB relative to the maximum gain value.
There are not many of them; an example is a lightning discharge. A winding containing 7 turns of wire is wound on top of it. That is, with constant current, it has one value, and with high-frequency currents it has a completely different value, differing many times. To effectively suppress such interference, capacitors C1 and C2 are used. Subscribe on Twitter! Electrical filters. Capacitive anti-aliasing filter
Filters
Designed to suppress interference. There are purely capacitive and inductive-capacitive ones based on LC circuits. Surge filter coils are available without cores or with ferrite cores (best on ferrite rings).
Additional devices. Indicators for switching on and the operational status of the protection on LEDs or neon bulbs glow when the filter (or its separate channel) is on and go out when the fuses trip. Arresters (gas) protect varistors at large amplitudes of impulse noise.
Any electrical appliance requires proper operation. There are also a number of safety rules regarding network filters. It is contraindicated to connect filters to each other.
Rice. 8. Example of a filter with Euro sockets.
This may unnecessarily increase the current in the ground wire. In addition, devices with high inrush currents (vacuum cleaners, air conditioners, refrigerators, etc.) cannot be connected to surge protectors. It is not recommended to connect surge protectors to uninterruptible power supplies as this may damage the protection circuits.
Petrovich35 › Blog › 220V surge protectors, what’s inside them
Good afternoon friends!
Almost all of us have at least one surge protector at home. Judging by the fact that the shelves of most stores selling electrical goods are littered with them, this is a popular item and is popular among the population (photo 1):
I have several similar filters in my home. There are some that are cheap and some that are more expensive. It all started with the fact that I decided to repair one of the burnt out filters, and then I became interested in studying the insides of other filters, and I disassembled several more. And as it turned out, not in vain. But first things first.
Firstly, they are convenient: in most cases, the surge protector is designed as an extension cord with several sockets, usually with a power switch on the housing. More advanced models also have built-in USB connectors for powering and charging various 5-volt gadgets.
So what kind of device do we buy in a box called “surge filter?” Can commercially available filters bear this proud name? As it turns out, the answer is not so clear-cut.
To answer this question, in this post we will look inside several similar devices, typical representatives of the most popular segment of the budget price category of about 400-700 Russian rubles ($6-$10).
What kind of lighting do you prefer?
Built-in Chandelier
Attention! Next there will be a lot of boring text and pictures. If you don't need details, read the conclusions at the end of the post.
Before moving on to specific filters, let's briefly refresh our memory about what kind of interference is found in a household single-phase AC 220V/50Hz network, i.e. in the sockets of our apartments and houses.
Let me remind you that this is not a lecture on electricity and electronics, but observations and reflections at the everyday level, so don’t pick too much on the terminology.
As is known, according to the standards in force in the Russian Federation, electricity supply organizations must provide electricity in the household network with an alternating voltage of 220V (more recently 230V) with a frequency of 50Hz of the correct sinusoidal shape.
Interference and distortion can be classified indefinitely, both by type and by the sources of their occurrence. Of course, a simple household filter cannot and is not required to cope with all of them. Therefore, for simplicity, so as not to get into unnecessary details, network interference, which in theory is feasible for a simple network filter, can be divided into two large categories:
Thus, we must understand that an ordinary household surge filter will not save you from long-term increases and decreases in voltage, or from changes in the nominal frequency of 50 Hz, or from on-air electromagnetic interference. All it can do is suppress high-voltage impulse noise and, at best, some of the network RF interference.
The operation process of a simple network filter is illustrated in Fig. 2:
But do inexpensive surge protectors live up to even these low expectations? Let's read what is indicated on the packaging of these filters (photo 3):
Basic parameters of network filters
Why is it important? Line filter with two-winding choke Capacitors are installed at the input and output of the circuit. So, with this universal filter, we hope everything is clear. You can also use a neon light bulb, for example, TN-0.2.
The circuit of a simple RC high-pass filter is shown in Fig. Try to determine the gain at this frequency from the frequency response in Fig. It is contraindicated to connect filters to each other. The FNRK varistor can be replaced with any one marked with the symbols “20K” or “20N” 20 is the diameter of the varistor in millimeters, - the varistor operating voltage is B.
The principle circuit of the high-frequency noise suppressor is shown in Fig. Filters Designed to suppress interference. And finally.
Inductance - 10 µH and above; The first two resistances are connected before the chokes to limit interference between the varistor and capacitors. Filters in power supplies for electronic...
