According to some embodiments, the negative injection circuit is configured to inject a negative voltage (?VDC) into the reference pin REF of the PFC controller 70, which also receives the sampled output voltage from the rectifier 40 (see FIG. 2C). The resulting waveform that is applied to the reference pin REF is a sum of the negative DC voltage and the sampled output voltage from the rectifier 40. The injection of the negative DC voltage, ?VDC, serves to shift the sampled signal downward so that the lowest voltage of the rectified signal reaches zero or approximately zero. The resulting peak of the rectified signal then becomes the maximum value Vmax minus the VDC injected by the negative injection circuit 100 (see FIG. 2D). In some examples, the resulting shifted waveform may be further scaled to compensate for any loss in peak voltage, for example, using a voltage-controlled resistor circuit. In some examples, the maximum value Vmax at the reference pin may be about 1.0 V to about 3.5 V (e.g., 1.25 V), the minimum voltage Vmin may be about 0 V to about 0.5 V, and the negative injection voltage ?VDC may be about ?1.0 V to about ?0.25 V.
According to some embodiments, the downshifting of the sampled rectified signal by the negative injection circuit 100 ensures that the power supply system 30 is able to operate efficiently by keeping the inductor current of the converter 50 in-phase and at the same fundamental frequency as the sampled rectifier voltage, thus providing a high power factor and low THD.
