PWM controller for standby efficiency

07 October 2008

IC is for soft switching asymmetrical half bridge topology.

The L6591 PWM controller for medium/high-power SMPS from STMicroelectronics enables designers to meet future regulations on standby power and operating efficiency.

The manufacturer claims that this is the world’s first integrated controller optimised for zero-voltage switching asymmetrical half-bridge converters, which enable smaller, lower-cost power supplies delivering high efficiency from standby to full load, thereby reducing heat and power loss.

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 operation at up to 500kHz. This allows small external filter components for compact overall dimensions. In addition, the IC implements pulse skipping under light-load and no-load conditions, and has a quiescent current lower than 3mA. Together, these properties allow designers to meet growing customer and end consumer demands 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.

According to the company, 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 US Government’s Energy Star programme. 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. Existing proposals look to increase this target in the future and the L6591 offers the ability to meet these tighter requirements.

In addition to its power-saving properties, the L6591 also has 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 UVLO (Under-Voltage Lock-Out) is also implemented, ensuring reliable operation of systems optimised for minimum no-load power.

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