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Intelligent circuit breaker development preferred SCR: ultra-small size, support 750V surge peak voltage

Technology Cover
Post Date: 2024-01-08, STMicroelectronics

The X0115ML is ST's first off-state surge peak voltage 750V compact thyristor (SCR) for Ground Fault Circuit Breakers (GFCI) and arc Fault Circuit Breakers (AFCI). The SOT23-3L micropackage (2.75mm x 3.10mm) is probably the smallest thyristor on the market today. Engineers can save a lot of board space while allowing industrial applications to have 600V off-state repeat peak voltages. In addition, the 1.1mm creepage distance meets the uncoated 120V AC insulation requirements of UL 840.

Why Design for Industrial GFCI and AFCI?

Design of life safety

According to the Bureau of Labor Statistics' Fatal Work Injury Survey for 2021, the most recent year for which data are available, of the 798 people who died from exposure to hazardous substances or the environment, electrocution was the second leading cause of death (152), after exposure to hazardous substances (551). In short, electrocution casualties are a real risk for factory workers and those working in industrial Settings, especially in the presence of water, and the degree of risk is so high that even a "small" current of 10mA can cause severe shock, while 50mA is enough to cause muscle contractions, bring about cardiac arrest, or cause respiratory distress.

Prevention of electric shock

In order to protect the safety of people's electricity, the National Electrical Code began to require the use of GFCI circuit breakers in residential equipment, and in 2000 introduced the high voltage industrial environment (480V to 600V) regulation. Most people are familiar with the traditional GFCI in circuit breakers. The system monitors the current of the live and neutral wires to determine whether the current coming out of the socket is returning to the ground wire. If the currents in the two wires are equal, everything is fine. If there is a discrepancy, the system assumes that the electricity is going somewhere else, for example, through an electrocuted human body. In this case, the GFCI will cause the circuit between the live line and the neutral line to trip, interrupting the current.

Electrical fire prevention

AFCI, on the other hand, monitors arc shape and arc amplitude to detect hazardous conditions and prevent electrical fires from occurring. As a result, the electronic design of AFCI is more complex than that of GFCI. Arc failures can be caused by loose wires or overheating or by current flowing through unexpected objects. All of these events produce high intensity and massive temperature surges that, if left unchecked, will trigger electrical fires. Corrosion or liquids can also cause arc failures, which can have serious consequences in an industrial environment.

Make the factory smarter

In addition to the national regulations applicable to such products, manufacturers are also designing smarter GFCI and AFC, connecting them to the cloud, collecting more data on electricity consumption, and automating operations. Remote circuit breaker reset is a very useful feature when you want to simplify equipment maintenance. However, these functions require more electronic components, such as microcontrollers, RF transceivers, sensors, etc. As a result, the new GFCI and AFCI must pack more components, but the board size must remain the same, which means engineers must look for smaller components in order to increase overall design density. However, given the critical characteristics of the product, they cannot sacrifice device performance and stability for smaller packages.

X0115ML, what should I pay attention to when integrating SCR rectifier in industrial GFCI or AFCI?

Grid triggers current


SCR is the core component of GFCI or AFCI, and gate sensitivity is the first technical feature of SCR that many people focus on. In the past, equipment in industrial environments could not be too sensitive, otherwise it would lead to false tripping, and the protection equipment would think that there was a fault, when in fact there was no fault. The reason is that with the significant increase of the power used by the equipment, the normal current change is significantly higher than that of the residential equipment. The X0115ML gate trigger current range is 30µA to 150µA, which is sensitive enough for a wide range of applications while still meeting industrial environmental standards.

Peak surge voltage

Another key indicator is the peak off-state surge voltage, which is a key indicator to determine the robustness of thyristors. In fact, in order to achieve the desired results, especially in industrial environments, the SCR must be able to handle very high peak voltages. Traditionally, the peak off-state surge voltage of high-power system devices is 700V, and the X0115ML rises to 750V. As a result, engineers can enjoy a greater voltage safety margin and can use ST devices in more devices. In addition, we offer stronger EMI protection measures to improve its robustness over its service life.

Package size and overall size

Finally, as the smart circuit interrupter market surges and the demand for electronic components increases, size becomes an increasingly important metric. Typically, industrial GFCI and AFCI are packaged in SOT-223 with SCR. Therefore, by switching to the SOT-23-3L package, we can reduce the overall device area to one-fifth of the standard package without compromising performance or UL 840 requirements. The X0115ML is even smaller than the X0115MUF, which has the same gate trigger current and direct surge voltage, except in a 5.6mm x 3.05mm SMBflat-3L package.

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