• • • SURGE + CIRCUIT PROTECTION • • •
Circuit Protection Solutions Using Semiconductor
Technology for IoT Devices Semiconductor technology using crowbar or avalanche junction transient voltage suppressor (TVS) devices contain a P/N junction with a larger cross section, which is proportional to its surge power rating. Longer duration pulses can be suppressed by increasing the die size and head dissipation. Both voltage and power capability can be increased by stacking parts in series or parallel. Package configurations for silicon thyristors or TVS diodes range from chip size to large module units. Semiconductor TVS devices can be unidirectional or bidirectional for voltages with positive and negative pulses. Semiconductor TVS devices have a sub-nanosecond response time as well as low clamping factors. These semiconductor devices do not wear out like classic MOV or GDT technologies and are available in a wide voltage range. These devices are very commonly used for protecting portable electronics, electronic interface I/Os as well as AC or DC power bus lines. Sub-nanosecond response times and low clamping voltages make these semiconductor devices highly effective. They also deliver long life performance in protecting electronics from the threats of ESD, EFT or surge transient sources.
Enabling Circuit Protection for
Common IoT Applications There are varied potential scenarios for transients to enter IoT systems and interrupt or damage operation of a functional IoT device, as is shown in Figure 5.
The IO Link protocol is widely used in IoT applications, such as Industry 4.0, for the deployment of sensors that may be monitoring temperature, pressure, humidity, etc. The sensors may be exposed to threats such as ESD, EFT, or surge transients. These threats can travel along lines to a central processing unit causing further damage. Any high voltage transient needs to be blocked/shunted to ground at the source and not allowed to damage downstream circuitry. A TVS solution shown in Figure 6 ensures that the IO link sensor is protected against ESD (plus or minus 8kV/15kV), EFT (4kV) and surge (1kV 24A 8/20us) transients.
important, removing the need to replace a sub-system can build an IoT brand’s quality reputation, particularly when compared with a competitor needing a sub-system replacement. IoT devices with antennae interfaces are potential points of contact for external ESD transients that could threaten the IoT system monitoring performance. Selecting the optimum capacitance of the protection solution is critical for high-speed transmission on ISM, Wi-Fi, or Bluetooth signals where high baud rates are required. The solution shown in Figure 9 ensures that antenna is protected against ESD (plus or minus 8kV/15kV) and EFT (4kV) transients while also providing ultra-low capacitance rates for data transmission.
Figure 6: Sensor IO LINK ESD/EFT/Surge Protection Figure 9: Antenna ESD Protection
RS-485 is the most versatile communication standard for IoT and widely used in a variety of applications. These include factory automation, building automation, HVAC, industrial process control, motor control, telecommunications equipment, security networks, sensors and metering.
Figure 5: Example of IoT Devices with Potential Ingress Areas of Transients
Another TVS solution shown in Figure 7 ensures that the RS-485 drivers and sensors are protected against ESD (plus or minus 8kV/15kV), EFT (4kV) and surge (1kV 24A 8/20us) transients. For AC line applications, it is possible to use a hybrid device which combines a TVS and thyristor semiconductor device. As a result, full resettable and long-life repeatable performance can be achieved for critical circuit protection applications. The hybrid device is triggered when the voltage reaches the breakover voltage and resets when the surge pulse is removed. Such a solution in practice is shown in Figure 8. It ensures that the AC/DC power supply is protected in accordance with IEC 61000-4-5 Class 2 L-L Surge (500V 250A 8/20us) transients. Such capabilities can reduce the costs of replacing sub-systems. Arguably more
IoT devices are embedded with sensors,
software, and connectivity capabilities that enable them to collect and exchange data over the Internet. The IoT market has opened doors to exciting new applications and opportunities for many markets and industries. The agriculture industry is already taking advantage of it. But it also brings unprecedented challenges that require thinking in new ways to meet mission-critical design requirements. Delivering successful IoT means overcoming common technical challenges and threats to performance. As a result, there is an ever demanding need to ensure greater safety and reliability for IoT devices operating in the field. Common ESD, EFT, surge, lightning, voltage spikes, or reverse polarity occurrences pose real threats with each new generation of devices. IoT system designers must consider adequate circuit protection solutions. But they must also ensure these solutions meet necessary compliance levels while allowing robustness of the IoT system for long life reliable performance in the field.
Figure 7 Sensor RS-485 ESD/EFT/Surge Protection
Figure 8: AC/DC PSU L-L Class 2 Surge Protection
electricalengineeringmagazine.co.uk
ELECTRICAL ENGINEERING • NOVEMBER 2024 39
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