The UCx907 family of load share controller ICs provides all the necessary features to allow multiple-independent-power modules to be paralleled such that each module supplies only its proportionate share to total-load current.

This sharing is accomplished by controlling each module’s power stage with a command generated from a voltage-feedback amplifier whose reference can be independently adjusted in response to a common-share-bus voltage. By monitoring the current from each module, the current share bus circuitry determines which paralleled module would normally have the highest output current and, with the designation of this unit as the master, adjusts all the other modules to increase their output current to within 2.5% of that of the master.

The current share bus signal interconnecting all the paralleled modules is a low-impedance, noise-insensitive line which will not interfere with allowing each module to act independently should the bus become open or shorted to ground. The UC3907 controller will reside on the output side of each power module and its overall function is to supply a voltage feedback loop. The specific architecture of the power stage is unimportant. Either switching or linear designs may be utilized and the control signal may be either directly coupled or isolated though the use of an optocoupler or other isolated medium.

Other features of the UC3907 include 1.25% accurate reference: a low-loss, fixed-gain current-sense amplifier, a fully differential, high-impedance voltage sensing capability, and a status indicator to designate which module is performing as master.