This article introduces…
1. Sources of Surge Voltage
1. Surge caused by lightning strikes, where the communication circuit generates induction, forming surge voltage or current;
2. Load switching and short-circuit faults in system applications can also cause surges;
3. High-frequency surge voltage caused by other devices frequently turning on and off.
According to some authoritative reports, there are more than 800 occurrences of surge voltages exceeding application voltage by more than double in a year, with over 300 occurrences of voltages exceeding 1000V. This is a significant number, averaging two occurrences per day, making surge protection circuits essential.
Figure 1
2. Why Power Supplies Need Surge Protection Circuits
The power module is the interface that contacts the system with the outside environment; all surges from the outside pass through the power module, hence the need for surge protection circuits.
Due to the small size and high integration of power modules, the maximum voltage and current tolerances of internal control chips and transistors are quite limited. A surge voltage can damage the module, leading to system paralysis. Even if there is no immediate damage, stress impacts on the components can affect their lifespan and reliability. Therefore, to ensure the continuous and reliable application of power modules, surge protection circuits are generally required. Many modules cannot include surge protection circuits internally due to size constraints, so external surge protection circuits need to be added.
3. Surge Testing Standards
The surge testing standard for power modules refers to IEC61000-4-5. This standard applies to the response of electrical and electronic devices to surge voltages generated by switching or lightning strikes at specified operating conditions. The standard does not test the high-voltage resistance of insulating materials nor does it consider direct lightning strikes.
The experimental level classifications of this standard are as follows:
Table 1 Experimental Levels
4. Surge Protection Circuits
Due to the small size of power modules, in high EMC requirement scenarios, additional surge protection circuits need to be added to enhance the EMC performance of the system and improve product reliability. As shown in Figure 2, to enhance the surge protection capability at the input level, varistors and TVS diodes are added externally. However, the circuits (a) and (b) in the figure aim to achieve dual protection but may backfire. If the varistor MOV2 in (a) has a lower voltage rating and current capacity than MOV1, in strong interference scenarios, MOV2 may fail to withstand the surge impact and get damaged prematurely, leading to system paralysis. Similarly, in circuit (b), due to the faster response speed of the TVS compared to the MOV, the MOV may not act while the TVS fails early. Therefore, the correct connection method is generally as shown in (c) and (d), with an inductor connected between two MOVs or between an MOV and a TVS.
Figure 2 Dual Surge Protection
As shown in Figure 3, a resistor can be added between the MOV and TVS to prevent the TVS from conducting and getting damaged before the MOV has a chance to act. When selecting R, the power consumption of R must be considered to avoid R failing first; at the same time, a capacitor can be connected in parallel to absorb energy and enhance surge resistance. The selection of MOV and TVS is crucial; choosing appropriate maximum allowed voltage and maximum current capacity is important, which should refer to the input voltage of the power module and surge test levels. If the voltage is chosen too low, the downstream power supply may not function properly; if chosen too high, it may not provide protection; if the current capacity is chosen too small, the components may easily get damaged.
Figure 3 Surge Protection
After selecting a reliable surge protection circuit, combined with ZLG’s third-generation new products, which are small in size, high efficiency, and come with short-circuit protection, to safeguard your system. For any inquiries, please feel free to add ZLG’s official customer service WeChat: zlgmcu-888.
Figure 4 Small Size High Efficiency SMD Products
ZhiYuan Electronics Introduction
Guangzhou ZhiYuan Electronics Co., Ltd., established in 2001, is a national-level high-tech certified enterprise and the Guangdong Provincial High-end Industrial Control Measurement Instrument Engineering Technology Research and Development Center.
Vision:To become a leading enterprise in the industrial internet ecosystem
Using “chips + AWorks software platform” to design high-value-added modules, boards, and high-end measurement instruments, connecting to the ZWS IoT cloud through wired and wireless interfaces, achieving big data processing, forming an industrial internet ecosystem.
Mission:To advance the process of China’s industrial internet with leading technology
Values:Professionalism and focus to achieve dreams
