Dual switch flyback solution provides alternative to LLC, single QR flyback topologies

August 02, 2011 // By Paul Buckley
Fairchild Semiconductor is offering a dual switch flyback solution incorporating mWSaver technology to meet these challenges faced by designers of power supplies for All-In-One(AIO) applications.

Traditional power topology solutions for AIO applications include LLC and single switch Quasi-resonant (QR) flyback. When balancing ease of design, power loss at different loading, and efficiency, each of these topologies has advantages and disadvantages. For AIO power range, LLC offers the best overall efficiency, compared to dual switch QR and single switch QR flyback converters. The LLC transformer is difficult to design and results in the highest light load power loss among the three topologies. Single switch QR flyback converters are the least efficient, but they are easy to design and offer low power loss at light load.

Fairchild's dual switch QR flyback topology and secondary synchronous rectification is the ideal solution for AIO applications - providing good overall efficiency, managing low power loss at light load, while providing ease of design.

The AIO solution from Fairchild is perfectly suited for applications from 75 W~230 W and consists of the FAN6920MR integrated critical mode PFC and Quasi-resonant Current Mode PWM controller, the FAN7382 gate driver, in tandem with the FAN6204 secondary synchronous rectifier controller for flyback topology and forward freewheeling rectification. Combined, these devices provide best-in-class power consumption at no/light load, enabling designs to meet 2013 ErP standard without the additional circuitry LLC solutions require.

Incorporating mWSaver technology, these devices additionally offer the lowest standby power input for AIO solutions. Quasi-resonant control reduces snubber and leakage inductance losses, while improving thermal issues. The device also lowers the Vds of the SR MOSFET to provide improved efficiency, and allows for smaller board size. Built-in two-level PFC output improves low line efficiency.

Adding the FAN7382, a high and low side gate drive IC, rounds out Fairchild's solution by providing the ability to drive Fairchild's High Voltage MOSFETs up to 600 V. This device provides stable operation of the high-side driver under high-dv/dt noise circumstances.

The FAN6920MR combines a power factor correction (PFC) controller and a quasi-resonant PWM controller for a cost