An analog implementation to improve load transient response of PFC pre-regulators

This paper presents an analog implementation to improve the load transient response of PFC pre-regulators. By means of a notch filter inserted between the output-voltage sensing network of the pre-regulator and the voltage control loop of the pre-regulator control circuitry, the bandwidth of the voltage control loop is greatly expanded without introducing extra input current harmonics into the pre-regulators. This approach uses operational amplifiers with R-C networks to realize the notch filter, therefore it can be implemented into the existing pre-regulators with minor modification. The notch filter can be applied in both continuous-conduction-mode (CCM) pre-regulators and discontinuous-conduction- mode (DCM) preregulators. Furthermore the size of the output capacitor of the pre-regulators can be reduced due to the expanded bandwidth of the voltage control loop. The improved load transient response of the analog notch filter is observed experimentally. A laboratory prototype of a 100W DCM flyback pre-regulator has been built to illustrate the benefits of this cost-effective solution.