9.3.1 Current Limiting and Overvoltage Protection and for Energy Meter Power Rails

Energy meters generally use a single AC/DC power supply (for example: flyback converter) with multiple DC outputs for powering blocks like Metrology (analog front-end, microcontroller, memory), Real Time Clock (RTC), Relay (for remote load connect/disconnect) and Communications module. Metrology is the most critical sub-system and is required to operate uninterrupted under all conditions, even if a fault occurs in any of the supplementary blocks. One solution would be to oversize the power supply design so that it can handle the excess current demands during a fault condition, which increases the cost of the meter. A more elegant and cost-optimized solution would be to add an eFuse like TPS2596xx on the supplementary power rails, which provides accurate current limiting and fast short-circuit protection, thereby ensuring reliable operation of the metrology block without increasing the size or cost of the power supply. Apart from that, the TPS2596xx provides additional benefits such as:

• Overvoltage Protection (Lock-out and Clamp) to shield down-stream low voltage circuits from harmful overvoltages arising from poor cross-regulation between windings or AC input voltage surges.
• Disconnect supply to rarely used loads to minimize power consumption

Figure 60 shows a typical energy meter power supply implementation using TPS2596xx.

Figure 60. Energy Meter Power Rail Protection Example

TIDA-010037 demonstrates energy meter design using eFuse for protecting auxiliary rails.