Single comparator based A/D converter for output voltage sensing in power factor correction rectifiers

This paper proposes a digital output voltage sensing method for power factor correction (PFC) rectifiers that requires only a single analog comparator and a small amount of digital hardware. Using this method a digital estimation of the output error voltage can be obtained at a rate of twice the line frequency (2fline) without the use of a traditional analog to digital converter (A/D). The proposed method effectively implements a windowed A/D around the output reference voltage with a window range equal to the magnitude of the ac output voltage ripple. When used in combination with a nonlinear-carrier (NLC) current controller, a power feedforward function is inherently embedded in the operation of the single-comparator A/D (SCA/D), which simplifies the voltage loop design and reduces voltage loop gain variation due to operating power level. Experimental results are reported comparing load transient responses using the SCA/D or a traditional A/D in a digitally controlled 300W boost PFC.