Dual Switch Synchronous QR Flyback Topology

Sep 14, 2011 10:05 AM

Fairchild Semiconductor offers a dual switch flyback solution incorporating mWSaver™ technology. 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 75W~230W 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. It 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 600V. 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 effective design that uses fewer external components. For PFC, the device uses a controlled on-time technique to provide a regulated DC output voltage and to perform natural power factor correction. With an innovative total harmonic distortion (THD) optimizer, the FAN6920MR can reduce input current distortion at zero-crossing duration in order to improve THD performance. For PWM control, the FAN6920MR provides several functions to enhance the power system performance, including extended valley detect up to the 12th valley cycle for reduced switching frequency, improved light load efficiency, green-mode operation, an internal 10ms soft start, and high/low line over-power compensation.

Using a proprietary linear prediction timing-control technique, not limited to the RDS(ON) of the external Fairchild power-trench SR MOSFET, the FAN6204 is suitable for fixed frequency or quasi-resonant (QR) flyback converters operating in discontinuous or continuous conduction mode (DCM and CCM) control. This technique includes a simple control method without current-sense circuitry, which provides better noise immunity. With PWM frequency tracking and secondary-side winding voltage detection, the device can operate in both fixed-and variable-frequency systems, making it adaptable to flyback and forward free-wheeling topologies. The FAN6204 also features an ultra-low green mode operating current (1.1mA typical). This internal green mode provides lower no-load power consumption and higher light-load efficiency.

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