AFCI Breaker Basics - The Necessity of AFCI Protection

What is an AFCI?

Arc Fault Circuit Interrupters (AFCI) are advanced circuit breakers specifically designed to prevent electrical fires by detecting hazardous arcing conditions in electrical circuits. They serve a vital role in modern electrical safety, offering a higher level of protection than traditional circuit breakers by monitoring the flow of electricity and identifying any abnormal arcing patterns that could potentially lead to a fire. When such a pattern is detected, the breaker trips and immediately shuts down the electrical circuit, mitigating the risk of fire caused by electrical arcs.

The Necessity of AFCI Protection

Incorporating AFCI protection in your electrical system is crucial for several reasons. Most importantly:

Preventing Electrical Fires: ARCIs are crucial in preventing fires caused by accidental arcs. These arcs can generate intense heat, igniting surrounding materials, and leading to serious fire hazards.

Enhanced Safety: By recognizing and reacting to unintended arc faults, AFCI breakers enhance the overall safety of your electrical setup, especially in areas prone to such faults.

Maintaining Circuit Integrity: Besides safety, AFCIs help maintain the reliability and integrity of your home's electrical system by preventing damage that can be caused by arc faults.

Products and reference designs of Products and reference designs

Our integrated circuits and reference designs help you create and optimize a residential circuit breaker design to support small form factor while accurately detecting faults and quickly disconnecting the load. We help you design a variety of residential breakers, including an arc fault circuit interrupter (AFCI), ground fault circuit interrupter (GFCI) or residual current circuit breaker (RCCB) that detects leakage currents, a surge protection device (SPD) that detects surges in voltages or a miniature circuit breaker (MCB) that detects fault current or temperature.

As shown in the figure below, AFCI consists of seven parts, each part is Non-isolated AC/DC power supply、Current sensing analog front end、Voltage sensing analog front end、Ground fault current sensing analog front end、MCU、Self-diagnostics/monitoring、Output user interface.

Non-isolated AC/DC power supply

DC voltage is derived from the main lines to power the breaker. Multiple architectures with different efficiencies are used to do the AC/DC rectification and regulation. Non-isolated AC/DC power supply includes Buck converters (integrated switch)、Flyback controllers、Linear & low-dropout (LDO) regulators, the corresponding products are LM5168、UCC28881、TLV709

Current sensing analog front end

Detection of an arc in the line current is done by looking at high frequency components. Depending on the range of frequencies, filters, log amplifiers and comparators can be used. Also, tripping an AFCI is a function of the magnitude of the current flowing through the line which is measured using the current sensing analog front end. Current sensing analog front end includes Comparators、Precision op amps (Vos<1mV)、High-speed op amps (GBW ≥ 50 MHz)、General-purpose op amps、Analog switches & muxes, the corresponding products are TLV7011、OPA2188、OPA835、TLV9052、TMUX4051

Voltage sensing analog front end

For measuring voltages and detecting zero cross over events voltage sensing analog front end can be used. Also, a comparator can be used to identify miswiring and alert the system. Voltage sensing analog front end includes Precision op amps (Vos<1mV)、Comparators、General-purpose op amps, the corresponding products are SM73307、TLV1851、TLV9002

Ground fault current sensing analog front end

Ground fault current sensing analog front end is used for monitoring leakages between line and neutral. If the leakage is above the thresholds defined in UL943 then tripping action is initiated. Ground fault current sensing analog front end includes Digital power monitors, the corresponding products are INA232

MCU

Advanced algorithms for detecting arcs faults are implemented using a microcontroller. Multiple peripheral such as ADCs, Timers, GPIOs dictate the MCU requirements. MCU includes MSP430 microcontrollers, the corresponding products are MSP430FR5994、MSP430FR5969、MSP430FR5992

Self-diagnostics/monitoring

A supervisor IC is used to monitor the power supply levels. It provides a fixed delay during a power glitch or when the reset function is forced upon the microcontroller. Self-diagnostics/monitoring includes Supervisor & reset ICs, the corresponding products are TPS3840、LM8364

Output user interface

LEDs are used for status indication. Output user interface includes RGB LED drivers, the corresponding products are LP5812、LP5810、LP5811