www.we-online.com/en CAPACITIVE DIGITAL ISOLATORS 21 www.power-mag.com Issue 3 2024 Power Electronics Europe Ensure Interference-free data communication Galvanic isolation of circuit components is required in many cases, especially in industrial environments. Capacitive digital isolators can be used to safely and reliably transmit user signals across an isolation barrier. The following circuit example shows how capacitive digital isolators can be used to galvanically isolate remote industrial equipment. For electronics in typical industrial environments interference-free data communication and personal safety are the two major challenges. Strong electromagnetic fields, overvoltages, transient voltages and high EMC interference are the order of the day. If, for example, the communication cable is laid unfavorably close to a control cable of a frequency inverter, the pulses are capacitively coupled in and the signals in the communication cable oscillate with the pulse pattern of the frequency inverter. This interference can quickly reach a level where significant malfunctions can occur and even endanger the safety of people. For example, when a thermocouple is used to measure the temperature of a motor, voltages in the millivolt range are generated. If these voltages are transmitted over a cable length of several meters to a central control unit that is referenced to a different ground potential, the measurement signal will be distorted by the potential differences. Summarizing the phenomena described, the following four challenges arise - Interference free data transmission - Separation of ground loops between spatial circuits - Minimize common-mode interference - A safety barrier between hazardous voltages and a user Figure 1 shows the situation of the data transmission system. In order to meet the requirements of shielding dangerous voltages from the user and still guarantee interference-free data transmission, galvanic isolation must be implemented to separate the zones electrically, i.e. in terms of potential, so that they can work separately and thus without interference. The data flow passes through the isolator. However, interference and potential equalization currents are prevented by the galvanic isolation. Isolated battery voltage measurement Distributed sensing of physical parameters is the state of the art, and powerful microcontrollers facilitate data processing. However, recording the data on the object is often a challenge, and wireless transmission of the data is often not possible. The data must be recorded on the object in such a way that the probe does not influence the variable to be measured, otherwise measurement errors will occur. This requires electrical decoupling, which must be implemented in the circuitry. Furthermore, the wired transmission of the data must be potentialfree and symmetrical so that the transmission is not disturbed by electromagnetic coupling and ground loops. In this application, the use of microcontrollers was deliberately avoided in order to demonstrate that a powerful, interference-free design can be implemented with little effort using analog circuit technology. The design is divided into two circuits, a transmitter and a receiver. The transducer can record a DC Figure 1: Basic concept of an isolated system for separating different potentials. Figure 2: Block diagram of the transmitter for potential-free voltage measurement.
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