At industrial communication sites, engineers are most concerned about transient overvoltages and overcurrents caused by surges in the communication network. These surges can lead to incorrect signals being sent across the bus or even cause system failure. To prevent such incidents, how should protection be designed from the beginning? This article will explore that.
First, let's understand what a surge is. In industrial environments, surges can result from lightning strikes, induced thunder surges, or switching operations in power systems—especially those with heavy inductive loads. These surges can generate transient overvoltages that affect the data bus, causing components to send erroneous signals and leading to significant losses for users. Therefore, lightning protection, surge suppression, and overvoltage protection are essential considerations in bus design. Today, we'll discuss common methods for protecting buses against surges.
There are two main types of surge protection: common-mode and differential-mode. Surges caused by lightning or high-current switching are typically common-mode. On the other hand, differential-mode surges often occur when high-voltage lines are close to data cables, especially if insulation between them is poor. Although differential-mode surges produce lower voltages and currents compared to common-mode surges, they can persist longer in the communication network. The nominal withstand voltage of an optocoupler or magnetic coupler is specified for common-mode voltages—the voltage between the input and output sides. If this is exceeded, both sides may be damaged. However, differential-mode voltages are not rated on components, and their tolerance depends on the circuit design. Exceeding the differential-mode limit can damage the front end without necessarily affecting the back end.
Second, traditional surge protection methods usually fall into two categories: isolation and diversion. Isolation methods use optocouplers or magnetic couplers to separate input and output signals. As long as the surge voltage doesn't exceed the device’s rating, it won’t be damaged—even if the surge lasts for a long time. However, this method only suppresses common-mode surges and cannot handle differential-mode surges. Diversion methods involve connecting the ground of the main equipment to a single point, allowing surge energy to be safely dissipated. Additional devices like TVS diodes, varistors, and gas discharge tubes (GDTs) are used to clamp the surge before it reaches the data port. When the clamping voltage is exceeded, these devices create a low-impedance path to divert harmful currents.
Combining isolation and diversion methods offers better protection. The diversion devices can suppress both common-mode and differential-mode surges, while the isolation devices protect the host equipment from common-mode surges. Together, they provide more comprehensive protection for the bus.
For example, CAN interface protection often involves using transceivers combined with isolation devices like optocouplers or magnetic couplers. For easier design, integrated transceiver modules are also available, offering simpler circuits and stronger environmental adaptability. While common-mode protection is widely used, this article focuses on improving differential-mode surge protection. Common diversion devices include GDTs, TVS diodes, and common-mode inductors. A typical configuration places the GDT at the front of the interface to provide first-level surge protection. When a surge occurs, the GDT quickly becomes conductive, creating a path for large currents and clamping the voltage between CAN_H and CAN_L to around 25V. The TVS then provides second-level protection, with specifications chosen based on requirements.
Third, an efficient surge protection solution is the module approach. While traditional circuits offer good protection, they require more components and can take up more PCB space. Improper component selection may also cause EMC issues. To address this, Zhiyuan Electronics has developed the SP00S12 signal surge suppressor. This compact module uses potting material combined with an isolation module to meet IEC61000-4-5 ±4KV standards. It is ideal for protecting signal ports in communication systems like CAN and RS-485, effectively suppressing surges caused by lightning and overvoltage.
Finally, comparing different methods reveals their strengths and weaknesses. Traditional methods rely on discrete components, while modern modules offer more compact and reliable solutions. Testing according to IEC61000-4-5 ensures that surge protectors meet required immunity levels. For instance, a 4kV common-mode surge test on the SP00S12 reduces the voltage to 17.1V at the output, demonstrating its effectiveness. These tests help ensure that surge protectors perform reliably under real-world conditions.
Shenzhen Kaixuanye Technology Co., Ltd. , https://www.icoilne.com