Poor system power factor at light load is caused by X capacitors that are used to reduce differential mode EMI being fed back to the AC line. HiperPFS-3 ICs incorporate a digital power factor-enhancing circuit that activates during light load conditions; this increases the compensation to overcome the reactance of X capacitors in the EMI filter, minimizing the phase angle difference between the input voltage and the current. Consequently, designers may increase the size of the X capacitors while minimizing or eliminating differential-mode chokes, thereby reducing EMI without degrading light load power factor performance. This results in a smaller, lower cost, EMI filter stage. Comments Edward Ong, product marketing manager at Power Integrations: "Standby energy-use standards such as ErP Lot 6 have previously forced designers of PCs and other systems to include both a main PSU and standby power supply.