Low Power Energy Metering Chip

Energy meters are usually directly floating on the live wire due to the direct current sensing (e.g. shunt resistors) and/or voltage sensing (resistance dividers). For safety’s viewpoint, the meters have to be isolated to protect human beings from 220 V power line. The isolation is usually accomplished by opto-couplers. There are two ways of isolations. One is to isolate the whole meter by floating the metering chip and MCU (Micro Control Unit) on the live wire and using opto-couplers to interface with communication modules and/or socket of IC (Intelligent Card) cards. The other is use opto-couplers to isolate the metering chips and the MCU such that the MCU is not floating on the live wire but share the ground with communication modules and/or socket of IC cards. There are pros and cons of each method. For the latter method, the MCU and energy metering chip must be powered in different domain, as energy meter chip must connect directly to power line. The following figure shows the block diagrams of single-phase meter and poly-phase metering having different power domain. In this kind of meters, the MCU and metering chip have to be in different power domain, and opto-couplers are inserted between MCU and meter chip for communication.