SLVAF85 September   2026 TPS2596 , TPS25961

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Conventional RC Circuit-Based Design
  6. 3Proposed Design with eFuse
  7. 4Comparison Summary and Conclusion
  8. 5References

1 Introduction

Technical advancements in smart-emeters have enabled advanced metering, demand tariff, and customer display for management. These advancements must be managed with less power consumption from the utility grid while maintaining the same form factor for the smart e-meter.

Single Phase Smart E-Meter Block Diagram Figure 1-1 Single Phase Smart E-Meter Block Diagram

A smart e-meter runs multiple internal modules, including the metrology core, central processor, communication modem,and latching relays as shown in Figure 1-1. While standard operations require minimal continuous power, the e-meter demands large power during wireless data transmission and the mechanical latching of the relay. Before quantifying the smart e-meter power requirements, it is useful to understand the operation of latching relay. The latching relay operation and its associated power requirements are described below .

Latching relays are used by the electrical utility operators to remotely connect/disconnect electric service for reasons, including emergency or immediate safety concerns, failure to pay bills, or even a service restart recharge of pre-paid accounts (prepaid e-meter). Relays requires a pulse of current to connect and disconnect the electrical services. During this, connect and disconnect events relay consumes peak power. The detailed power consumption analysis is given below .

  • Typically, a 12V coil latching relay is used in smart e-meters.
  • The power requirement for such a relay range from 3W to 6W for 100ms in a single-phase smart e-meter, and from 4.5W to 9W for 100ms in a three-phase smart e-meter.
  • The pulse duration requirement varies between 50ms and 100ms, depending on the relay manufacturer.

The specifications of IM901 relay from Ivy Metering are provided in Table 1-1.

Table 1-1 Specifications of IVY Metering IM901 Relay
Nominal coil operating voltage (V) Minimum operating voltage (V) Single Coil resistance (Ω)
6V 0.2V 24Ω
9V 6.3V 54Ω
12V 8.4V 96Ω
24V 16.8V 384Ω
48V 33.6V 1536Ω

In a typical smart e-meter, communication modem and latching relay are the critical power consuming components .A typical communication modem and latching relay consumes a peak power of 8W and 6W respectively. So, the total combines peak power requirement of these loads is 14W.

There are two ways to address this peak power requirement as discussed below:

  1. Option 1: Customized 15W SMPS Design

    In this approach, the power supply is designed to directly meet the full peak power requirement. The customer must go with a 15W Switch mode power supply design with typically EE22-based transformer, two 68uF 400V bulk capacitor in series, bigger EMI filter resulting in larger PCB size and cost.


  2. Option 2: Standard 11W SMPS Design

    In this approach, the power supply is sized for the average load, while peak relay energy is supported by a hold-up capacitor.

    Option 2 is preferred by manufacturers because of its size and cost effectiveness which will be discussed in the next section.