Fairchild Semiconductor International expands its market leadership in products for power factor correction by introducing the FAN4822 PFC controller, targeted for power supplies of 500W or more. The FAN4822 is an average-current boost-type device employing zero-voltage switching (ZVS) control circuitry designed for efficient operation at high switching frequencies. The continuous boost architecture allows designs to achieve the high power factor (up to 98%) and the low total harmonic distortion (THD) necessary to comply with "green" initiatives, such as the IEC 1000-3-2 standard for energy efficiency and noise reduction in consumer electronics. The built-in ZVS circuitry allows designers to use smaller, lower cost components to save board space while reducing switching losses and noise caused by electromagnetic interference (EMI).

Fairchild's broad portfolio of PFC and PFC/PWM combo chips for medium and high-power supplies is recognized as the market leader in solutions for power factor correction. The FAN4822 offers exceptional performance and strengthens Fairchild's position in high-power applications, such as servers, routers, power supplies, and telecom switching equipment.

Safety features on the FAN4822 include under-voltage lockout, over-voltage protection (to eliminate output "runaway" due to load removal), peak-current limiting, and input-voltage brownout protection. The FAN4822 is rated for operation over the -40ýC to +85ýC temperature range, and is available in 14-lead plastic DIP and wide-body 16-lead SOIC packages.

Analog and Mixed Signal Products Group, Fairchild Semiconductor International 3001 Orchard Parkway o San Jose, CA 95134. Tel: 408-822-2314; Fax: 408-822-2410. Customer Support Center Tel: 888-522-5372. Web: www.fairchildsemi.com.

Fairchild just improved on their power factor correction control design with this product that will be a favorite with many designers. This power factor controller identifies limitations inherent in the continuous conduction mode boost converter topology, and offers a solution. The higher operating frequencies allow for smaller filter components both at the output and input filter. This reduces cost and increases packaging density. The fundamental limitations on the operating frequency of continuous conduction mode boost converters are the reverse recovery current associated with the boost diode and the switching losses associated with the FET output capacitance. At frequencies above 100kHz these losses become excessive.

A typical method for reducing reverse recovery currents is the addition of an inductor (L2) in series with the main switching transistor (see Figure 1). Inductor L2 requires an equivalent volt-seconds during the off time for proper reset. This method requires a tapped boost inductor to provide the extra voltage required for reset. Also, L2 must carry the same current seen by the main FET. Although this method does provide significantly reduced reverse recovery currents, it does not eliminate the switching losses associated with the capacitance at the drain node being discharged by the FET.

Figure 1

Fairchild now offers a zero voltage switching technique that eliminates the diode recovery problem and significantly reduces FET switching losses with their zero voltage switching power factor control IC. It makes sense because they operate at a higher frequency which offers better efficiency and lower electromagnetic interference. The device is able to implement the zero voltage switching with an additional gate drive output. The zero voltage switching circuitry consists of an additional switching FET, resonant inductor and capacitor, and a clamping diode necessary for resetting the resonant inductor (see Figure 2).

Figure 2

The RMS current seen by the zero voltage switching Q is small. An ultra low RDS-on FET is not necessary, but the capacitance of the zero voltage switching Q is important. A device with reduced capacitance (higher RDS-on) is needed to reduce switching losses. Fairchild says that efficiency improved from 87% (without zero voltage switching) to 92% with it at 120VDC input. At 370VDC input the efficiency, with or without zero voltage switching operation, is roughly 95%. You can find much more detailed information in a Fairchild application note.

14-lead PDIP (FAN4822IN) and 16-lead SOIC (FAN4822IM) U.S. $3.21 (1,000 pieces.). Availability: Now. Delivery:8-10 weeks ARO.