STMicro Releases Integrated Controller For Soft-Switching Asymmetrical Half-Bridge Topology
STMicroelectronics introduced its L6591 PWM controller – described as as the first integrated controller optimized for zero-voltage switching asymmetrical half-bridge converters, which are said to 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 minimizes EMI emissions, and also enables efficient operation at up to 500kHz. This allows small external filter components for compact overall dimensions. In addition, the L6591 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 minimize 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 maximize 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 1Watt plan for standby power, the EU’s EuP Directive for energy-using products, and the US Government’s Energy Star program.
Regulations such as EuP and Energy Star now call for minimum operating efficiency of 85% 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 headroom to meet these tighter requirements.
In addition to its power-saving properties, the L6591 also has comprehensive built-in protection, including pulse-by-pulse over-current protection to prevent false tripping, overload protection with latched or auto restart behavior, and transformer-saturation detection. Adaptive Under-Voltage Lock-Out (UVLO) is also implemented, ensuring reliable operation of systems optimized for minimum no-load power.
The L6591 combines its high integration and comprehensive power-saving features with high voltage-handling capability, up to 700V, in a small-outline SO16N surface-mount package. Devices are available in production quantities, at prices from $1.50 in quantities of 2500 pieces.
