The most simple approach for electrical power factor correction is a passive solution with filtering via a large iron choke. This is generally only practical for relatively low power circuits, due to the size and cost, and is falling out of favor due to improvements in active converter cost. The charge pump circuit is a quasi-active approach, using an existing switching transistor to transfer power through a capacitor to the power bus capacitor. The incremental component cost is fairly low but the regulation is poor with output voltage dependent on the load. This approach works best with converter types such as the Quasi resonant flyback with load dependent switching frequency. Finally, the fully active approach uses a separate power converter such as a boost converter, flyback converter, or buck-boost converter to draw current from the AC line in a resistive fashion and regulate the bus capacitor voltage against variations from load current changes.