AC-DC Power Supplies are often operated in parallel to achieve increased power, as well as to provide fault tolerance through redundant operation. Electronic circuitry is generally employed to assure current sharing between parallel-connected modules. These circuits generally fall into two alternate strategies: active current share via an interconnect wire (or bus), or passive sharing via the output droop method. This paper explores operation with droop share and illustrates how this method provides extremely accurate sharing with minimal complexity.
Modern powering architectures for Telecom and Network equipment solutions utilize multiple paralleled switch mode power supplies (for the first level of power conversion AC/DC) to reach the required output power rating. When multiple power supplies are connected in parallel, current sharing is desired. As the name suggests, this ensures that modules connected in parallel each share a portion of the total system load. The advantages of this feature include higher reliability of individual modules as a function of the lower overall temperature and better regulation.
To implement current sharing between modules, their output voltages need to be perfectly matched, under all conditions. However, in the real world, it’s nearly impossible to achieve the required set-point accuracy. The power supply designer has a choice of methods to achieve module current sharing: