Apparatus and method for sharing a load current among

Abstract

A current sharing circuit forces current delivered to a common load to be provided in substantially equal shares by two or more D.C.-to-D.C. converters, particularly those of the type whose output varies according to a predetermined functional relationship with the frequency of a controllable signal generated by the converter indicating its operating frequency. The load current delivered by such converters typically varies approximately proportionately with the converter operating frequency when the converter input and output voltages are held constant. Based on the frequency of these indicating signals and the predetermined relationship between their frequency and the output current of each respective converter, it is determined which particular one of the converters is presently supplying the largest share of load current. The outputs of each of the other converters are adjusted to share the load more equally among all the converters. In the preferred embodiment a frequency to voltage converter senses the operating frequency and converts it to a filtered analog voltage which is functionally related to the input frequency. An amplifier circuit compares this analog signal with the same signal from other D.C.-to-D.C. converters. The error signal is used as a control signal to adjust the converter output voltage to force the analog signal to be substantially equal to the analog signals from other D.C.-to-D.C. converters, which in turn, forces the operating frequencies and currents delivered to the common load by each converter in the system to be substantially equal.