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Dual switch flyback converter targets AIO apps

Posted: 04 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:dual switch flyback? transformer? power consumption? AIO application?

In order to meet global energy policies and the challenge of limited space and providing ease of design for power supplies of All-In-One (AIO) applications, Fairchild Semiconductor International Inc. has unleashed a dual switch flyback solution.

According to the company, its dual switch quasi-resonant (QR) flyback topology and secondary synchronous rectification is the ideal solution for AIO applications from 75C230Wproviding good overall efficiency and best-in-class power consumption at no/light load. The solution consists of the FAN6920MR integrated critical mode PFC and QR current mode PWM controller, the FAN7382 gate driver, in tandem with the FAN6204 secondary synchronous rectifier controller for flyback topology and forward freewheeling rectification. These devices combined enable designs to meet 2013 ErP standard without the additional circuitry LLC solutions require, the company added.

The devices that integrate the mWSave technology offer the lowest standby power input for AIO solutions while the QR control reduces snubber and leakage inductance losses and improves thermal issues, Fairchild noted. 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.

The FAN7382, a high and low side gate drive IC, can drive Fairchild's MOSFETssuper-junction SupreMOS and SuperFET. The company's high-voltage (up to 600V) process and common-mode noise cancelling technique provides stable operation under high dv/dt noise circumstances. An advanced level shift circuit allows high-side gate driver operation up to VS = -9.8V (typ.) for VBS = 15V. The input logic level is compatible with standard TTL-series logic gates while UVLO circuits for both channels prevent malfunction when VCC and VBS are lower than the specified threshold voltage.

The FAN6920MR combines a power factor correction (PFC) controller and a QR PWM controller for a cost effective design that uses fewer external components. The device uses a controlled on-time technique to provide a regulated DC output voltage and to perform a natural PFC. The FAN6920MR can reduce input current distortion at zero-crossing duration in order to improve THD performance with an innovative total harmonic distortion (THD) optimizer. 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, internal 10ms soft start and high/low line over-power compensation, the company said.

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 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 that provides better noise immunity, Fairchild explained. 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 freewheeling 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, the company added.

Fairchild Semiconductor enables engineers to drive innovation in their designs by offering smaller size and increased performance through advanced silicon and package options. The price of FAN6920MR is $1.20, FAN6204 is $0.57 and FAN7382 $0.83 in 1,000 quantity pieces with delivery of 8C10 weeks ARO.

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