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PWM controller suits offline power supplies

Posted: 26 Sep 2008     Print Version  Bookmark and Share

Keywords:integrated controller  power supplies  Zero-voltage switching  half-bridge converter 


STMicroelectronics has introduced the L6591 PWM controller, which the company claims as the first integrated controller optimised for zero-voltage switching asymmetrical half-bridge converters. The device enables smaller and lower-cost power supplies, delivering high efficiency from standby to full load, which results in reduced heat and power loss, said STMicro.

For use in offline power supplies, the L6591 implements all of the functional blocks necessary to control a soft-switching half-bridge converter. Zero-voltage switching eliminates turn-on switching losses and minimises EMI emissions, and also enables efficient operation at up to 500kHz. This allows for the use of small external filter components. In addition, the L6591 implements pulse skipping under light-load and no-load conditions, and offers a quiescent current lower than 3mA.

Together, these properties allow designers to meet growing requirements to minimise power dissipation in standby modes as well as when fully operational. For power-factor-corrected systems, the L6591 also provides a PFC interface, allowing the PFC pre-regulator to be turned off to maximise power savings under light- and no-load conditions.

Using the L6591 with the zero-voltage switching asymmetrical half-bridge topology, designers can ensure compliance with regulations such as the International Energy Authority's 1W plan for standby power, the EU's EuP Directive for energy-using products, and the U.S. government's Energy Star program. Regulations such as EuP and Energy Star now call for minimum operating efficiency of 85 per cent in power supplies for equipment such as PCs, servers, consumer products, and general-purpose ac/dc adapters and chargers.

In addition to its power-saving properties, the L6591 also offers comprehensive built-in protection including pulse-by-pulse over-current protection to prevent false tripping, overload protection with latched or auto restart behaviour, and transformer-saturation detection. Adaptive Under-Voltage Lock-Out (UVLO) is also implemented, ensuring reliable operation of systems optimised for minimum no-load power.

The L6591 also provides a high-voltage-handling capability, up to 700V, in a small-outline SO16N surface-mount package.

-Gina Roos

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