DC eMeter SMPS design for telecom shelters

A cell site/telecom shelter consists of electronic infrastructure which includes base station, microwave radio equipment, switches, antennas, transceivers for signal processing and transmission, and non-electronic infrastructure which includes tower, shelter, air-conditioning equipment, diesel electric generator, battery, electrical supply and so on.

The AC and DC energy consumption for different operators and competitors depends on the load connected to it. DC energy consumptions for loads like BTS, Microwave, and so on is calculated using a DC energy meter by connecting appropriate shunts in the negative path of loads. The voltage drop across the shunt is fed to DC energy meter input terminals. The DC Energy Meter is a micro-controller based product which measures Battery DC voltage, 4 channels DC currents for different operators and displays them on a 16x2 backlit LCD.

The DC Energy Meter also requires an isolated RS-485 port for communication with the master device using MODBUS-RTU protocol. This calls for two output power supplies; a non-isolated +5 V at 200 mA–400 mA, and an isolated +5 V at 100 mA for RS485 interface with input DC voltage varying from 12 V to 75 V as the batteries can be 24 V or 48 V.

An isolated buck converter (fly-vuck) uses a synchronous buck converter, LM5017, with coupled inductor windings to create isolated outputs. Isolated converters utilising Fly-Buck topology use a smaller transformer, no need for an optocoupler or auxiliary winding as compared to a flyback converter, resulting in a smaller solution size and cost.

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Originally published by Texas Instruments Inc. at www.ti.com as "DC E-Meter SMPS Design Using LM5017 in Isolated Buck Topology for Telecom Shelters".