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 (2(fline)) without the use of a traditional analog to digital converter (AID). The proposed method effectively implements a windowed AID 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 AID (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 AID in a digitally controlled 300W boost PFC.