The MC34261/MC33261 are active power factor controllers specifically designed for use as a preconverter in electronic ballast and in offline power converter applications. These integrated circuits feature an internal startup timer, a one quadrant multiplier for near unity power factor, zero current detector to ensure critical conduction operation, high gain error amplifier, trimmed internal bandgap reference, current sensing comparator, and a totem pole output ideally suited for driving a power MOSFET. Also included are protective features consisting of input undervoltage lockout with hysteresis, cyclebycycle current limiting, and a latch for single pulse metering. These devices are available in dualinline and surface mount plastic packages.