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Дома > Список технологий > What thing should we notice when choosing a circuit protection device

What thing should we notice when choosing a circuit protection device

Время публикации: 2019-02-16

As electronic products integration, processor speed, switching speed, and interface speed continue to increase, ESD/EMI/EMC issues are becoming more and more prominent, especially when handheld electronic devices are moving in a thin and light direction and their product functions are increasing.

The number of input/output ports also increases, causing electrostatic discharge to enter the system,then interfering with or damaging the integrated circuit.

It can be seen that it is easy to have problems in circuit protection and it is easy to be ignored.

In the fields of communication, consumption, military, aerospace, ESD is often the culprit causing circuit failure. How to choose over-current,over-voltage protection device, eliminating conducted-radiation electromagnetic interference, constructting EMC test environment,etc.they are all difficulties for engineers in design.

So how to solve these problems? Let us discuss it today.

The development of circuit protection components in the future

Circuit protection components typically include both overvoltage protection devices and overcurrent protection devices. Engineers need to make choices based on component characteristics and application types.

In electronic products, the density of printed circuit boards continues to increase, and the operating voltages of semiconductor components and integrated circuits continue to decrease. Manufacturers use small technologies such as surface mount technology, chip multilayer ceramic technology, and array technology to develop small sizes and meet the requirements. Small voltage high current circuit protection products required.

It is foreseeable that in the future, electronic power technology will continue to develop, and manufacturers of circuit protection components will continue to vigorously develop new products and technologies to provide suitable and safe circuit protection components for various application fields.

Why is it important to choose the right circuit protection device?

Choosing the right circuit protection device is the key to achieving efficient and reliable circuit protection design. When it comes to the selection of circuit protection devices, we must know the role of each circuit protection device. When choosing a circuit protection device, we must know that the protection circuit should not interfere with the normal operation of the protected circuit. In addition, we must also prevent any voltage transients from causing repetitive or non-repetitive unstable behavior of the entire system. We need to perform multiple simulation tests to achieve the reliability and usability of the circuit protection solution.

How to choose a circuit protection device, here are some tips.

In the face of the great harm caused by ESD, overvoltage, surge, overheating, etc., the latest circuit protection devices not only need to pay attention to volt-ampere characteristics, protection level and other factors, but also consider many other problems.

For example, electronic devices are becoming thinner and lighter. In order to meet the size constraints and provide circuit protection in a smaller footprint, protection device manufacturers need to develop smaller components, which requires manufacturers to continuously improve the energy  density of components.

When the interface speed of electronic devices continues to increase, in order to ensure signal integrity, the size of the protection device capacitor must be considered. The protection scheme must follow the development trend of the interface to ensure the reliability of the interface, and at the same time ensure the impact resistance of the protection components. Anti-seismic, moisture-proof and other factors.

Circuit protection concept map

Type of circuit protection device

Although there are many types of protection devices, they can be divided into overcurrent protection and overvoltage protection. 

How the fuse works

The most important overcurrent protection device is a fuse.It is generally connected in series in the circuit, requiring a small resistance. When the circuit works normally, it is only equivalent to one wire, which can stably turn on the circuit for a long time, and current fluctuation occurs due to power supply or external interference. It can also withstand a certain range of overload. Only when the circuit through a large overload current(fault or short circuit) , the fuse will operate, and the circuits is protected by breaking the current to avoid the danger of product burnout.

In the process of breaking the circuit of the fuse, due to the existence of the circuit voltage, an arc will occur at the moment of melt disconnection. The high-quality fuse should avoid such arcing as much as possible.

After breaking the circuit, the fuse should be able to withstand the circuit voltage applied at both ends.

The fuse is subject to pulse damage and will gradually reduce the ability to withstand the pulse. The necessary safety margin must be considered when selecting; this safety margin refers to the fuse The total blown time, which is the sum of the pre-arcing time and the arcing time.

Therefore, when selecting, you need to pay attention to the basic conditions of its melting characteristics and rated current; in addition, the environment around the fuse should be considered in the installation, and the fuse will only be blown when it reaches its own melting heat value, if it is cold in the environment. In its condition, its melting time will change, which must be taken care of when using it.

EMC test points

Electromagnetic compatibility (EMC) refers to the state in which a device or system does not degrade in an electromagnetic environment. EMC, on the one hand, there is no serious interference source in the system, that is, the electromagnetic interference generated by the equipment in the environment during the normal operation cannot exceed a certain limit. On the other hand, the equipment or the system itself has better anti-electromagnetic interference. That is to say, the appliance has a certain degree of immunity to electromagnetic interference existing in its environment, that is, electromagnetic sensitivity.

EMC includes EMI and EMS:

1) EMI, electromagnetic interference, is the electromagnetic noise generated by the machine itself in the process of performing its functions, which is not conducive to other systems.

2) EMS refers to the ability of a machine to be unaffected by the surrounding electromagnetic environment during the execution of its intended function.

How to eliminate electromagnetic interference?

Electromagnetic interference refers to electromagnetic waves generated during the working process of an electronic device and is emitted externally, thereby causing interference to other parts of the device or other external devices. 

To cause electromagnetic interference, the system must have three factors, namely electromagnetic interference source, coupling path, and sensitive equipment.

Therefore, to solve the electromagnetic interference problem, it is necessary to solve the electromagnetic compatibility problem by removing one of the factors from these three factors. Commonly used effective methods are: grounding technology, shielding technology, filtering technology.

The description of Grounding technology

Grounding technology can be divided into working grounding, lightning protection grounding and protective grounding.

The working grounding is to directly ground the neutral point in the three-phase power supply in the low-voltage AC grid.

In the communication station, there are usually two kinds of lightning protection grounding: one is a lightning rod lightning protection grounding device specially designed to protect buildings or antennas from lightning strikes, which is designed and installed by the construction department, and the other is to prevent A lightning protection grounding device embedded in a lightning arrester for lightning or overvoltage damage to a communication device or a power supply device.

The protective grounding is a good electrical connection between the metal casing part of the powered device that is normally insulated from the live part and the grounding device.

The description of Shielding technology

The electromagnetic shielding technology in the circuit mainly survives in a common electromagnetic environment, and the electromagnetic interference suppression technology is used to prevent interference from other factors in actual work.

Shielding technology mainly uses a complete metal shield to surround the dotted conductor to improve the sensing capability of the shield.

The description of Filter technology

The filter is one of the indispensable key components in the RF system. It is mainly used for frequency selection, allowing the required frequency signal to pass and reflecting the unwanted interference frequency signal.

Filtering technology is mainly divided into signal filtering and EMI filtering.

Signal filtering is the known input and output impedance, while attenuating out-of-band interference, while ensuring extremely low insertion loss in the passband.

EMI filtering is within the range of the desired operating frequency bandwidth, the range of variation of the termination impedance will increase, and the insertion loss affected by the loading current is determined by the ability to suppress external interference signals.

You can buy related circuit protection components, filters, etc. at jotrin electronics mall.

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