In circuit design, some design methods for circuit protection

Do you know some issues in circuit design 1? In circuit design, circuit protection is a part that is prone to problems and is also an issue that is easily overlooked. Often in the fields of communications, consumer, military, aerospace and other fields, ESD is often the culprit causing circuit failure. Issues such as overcurrent and overvoltage protection device selection, conducted radiation electromagnetic interference elimination, and EMC test environment have become difficulties for engineers during design. , how to solve these problems? Follow the editor to find out!

1. Circuit protection starts with component selection

Circuit protection components usually include overvoltage protection devices and overcurrent protection devices. Engineers need to choose based on the characteristics of various components and different 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 new technologies such as surface mount technology, chip multi-layer ceramic technology, and array technology to develop small-sized products that meet the needs of small customers. Products that meet the needs of high-voltage and high-current circuit protection; it is foreseeable that in the future, electronic power technology will continue to develop, and domestic and foreign circuit protection component manufacturers will continue to vigorously develop new products and new technologies to provide suitable and safe circuit protection components for various application fields. device.

Selecting appropriate circuit protection devices is the key to achieving 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 selecting circuit protection devices, we need to know that the protection circuit should not interfere with the normal behavior of the protected circuit. In addition, it must also prevent any voltage transients from causing repetitive or non-repetitive unstable behavior of the entire system. Conduct multiple simulations. Testing to achieve the reliability and practicality of circuit protection solutions.

2. Selection skills of circuit protection devices

Faced with the huge harm caused by ESD, overvoltage, surge, overheating and other phenomena, new circuit protection devices need to consider many other issues in addition to factors such as volt-ampere characteristics and protection levels. For example, electronic devices are becoming thinner and thinner. In order to comply with size restrictions 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 equipment continues to increase, the capacitance of the protection device must be considered to ensure signal integrity. The protection scheme must follow the development trend of the interface to ensure the reliability of the interface, and at the same time, the impact resistance of the protection components must be guaranteed. Earthquake resistance, moisture resistance and other factors.

3. Characteristics of overcurrent and overvoltage protection devices

Although there are many types of protection devices, functionally they can be divided into overcurrent protection and overvoltage protection. One of the important overcurrent protection devices is the fuse, also called a fuse. It is generally connected in series in the circuit, and its resistance is required to be small (low power consumption). When the circuit is working normally, it is only equivalent to a wire, which can conduct the circuit stably for a long time. Current fluctuations occur due to power supply or external interference. It should also be able to withstand a certain range of overload. Only when a large overload current (fault or short circuit) occurs in the circuit, the fuse will operate and protect the safety of the circuit by cutting off the current to avoid the risk of product burnout. .

When the fuse breaks the circuit, due to the presence of circuit voltage, an arc will occur at the moment the melt breaks. A high-quality fuse should try to avoid this arcing; after breaking the circuit, the fuse should be able to withstand The circuit voltage applied to both ends. Pulse damage to the fuse will gradually reduce its ability to withstand pulses. The necessary safety margin needs to be considered when selecting it; this safety margin refers to the total fusing (action) time of the fuse, which is the pre-flight The sum of arc time and arcing time.

Therefore, when selecting, you need to pay attention to its fusing characteristics and rated current. In addition, you must consider the environment around the fuse when installing. The fuse will only melt when it reaches its own melting heat energy value. If the environment is cold, Under certain circumstances, its fusing time will change, which must be paid attention to when using it.

4. Key points of EMC testing

Electromagnetic compatibility (EMC) refers to the state in which the performance of a device or system does not degrade in the electromagnetic environment. EMC, on the one hand, requires that there are no serious interference sources in the system, that is, the electromagnetic interference generated by the equipment on the environment during normal operation cannot exceed a certain limit, on the other hand, it requires that the equipment or system itself has good anti-electromagnetic interference, that is, Appliances have a certain degree of immunity to electromagnetic interference existing in their environment, that is, electromagnetic susceptibility.

EMC includes two parts: EMI (electromagnetic interference) and EMS (electromagnetic tolerance):

1. EMI electromagnetic interference is the electromagnetic noise generated by the machine itself in the process of performing its functions that is detrimental to other systems.

2. EMS refers to the ability of a machine to not be affected by the surrounding electromagnetic environment while performing its intended functions.

5. How to eliminate electromagnetic interference?

Electromagnetic interference refers to the electromagnetic waves generated by electronic equipment during its own working process, which are emitted externally, causing interference to other parts of the equipment or other external equipment. For electromagnetic compatibility problems, that is, electromagnetic interference, to occur in a system, three factors must exist: electromagnetic interference sources, coupling pathways, and sensitive equipment. Therefore, when solving the problem of electromagnetic interference, we must focus on these three factors and prescribe the right medicine to eliminate one of the factors to solve the electromagnetic compatibility problem. Commonly used effective methods include: grounding technology, shielding technology, and filtering technology.

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

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

In a communication bureau (station), there are usually two types 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 a lightning protection grounding device designed to protect buildings or antennas from lightning strikes. It is a lightning protection grounding device that is buried by installing a lightning arrester in order to prevent damage to communication equipment or power supply equipment due to lightning overvoltage. Protective grounding is a good electrical connection between the metal shell part of the powered equipment and the grounding device that is insulated from the live parts under normal circumstances.

2. Shielding technology: The electromagnetic shielding technology in the circuit is mainly to survive in a common electromagnetic environment. By using electromagnetic interference suppression technology, it prevents interference from other factors in actual work, resulting in irrational application of technology.

Shielding technology mainly uses a complete metal shield to surround a conductor with a point to improve the induction capability of the shield and ensure that the same charge as the charged conductor can appear on the outside. If the charge on the outside flows into the earth, there will be no electrical leakage on the outside. , and the better the conductive performance of the metal shield, the better the shielding effect of static electricity. Shielding technology needs to play a shielding role through grounding.

3. Filtering technology: Filter is one of the indispensable key components in the radio frequency system. It is mainly used for frequency selection, allowing the required frequency signals to pass and reflecting the unnecessary interference frequency signals.

Filtering technology is mainly divided into signal filtering and EMI filtering: signal filtering ensures extremely low insertion loss in the passband while attenuating out-of-band interference when the input and output impedances are known. EMI filtering is within the desired operating frequency bandwidth, and the variation range of the termination impedance will increase. The insertion loss affected by the loading current is determined by the ability to suppress external interference signals. The above are some solutions for protecting circuits. I hope they can help you.