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PWM controller ensures better standby mode capacity

Posted: 26 Sep 2008 ?? ?Print Version ?Bookmark and Share

Keywords:controller? converter? PFC interface?

STMicroelectronics has released the L6591 PWM controller, which the company claimed is the first integrated controller intended for zero-voltage switching asymmetrical half-bridge converters. STMicro said the device provides smaller and lower-cost power supplies, rendering high efficiency from standby to full load, resulting in decreased heat and power loss.

When used in offline power supplies, the controller has the functional blocks needed to control a soft-switching half-bridge converter. Zero-voltage switching removes turn-on switching losses, reduces EMI emissions, and also provides efficient operation of up to 500kHz. This permits the use of small external filter components. In addition, the L6591 manages pulse skipping under light-load and no-load conditions, and gives a quiescent current lower than 3mA.

These properties help designers to meet the necessary requirements to reduce power dissipation in standby modes as well as when fully operational. For power-factor-corrected (PFC) systems, the L6591 also provides a PFC interface, letting the PFC preregulator to be turned off to maximize power savings under light-load and no-load conditions.

Employing the L6591 with 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 Enery-using Products (EuP) Directive, and the U.S. government's Energy Star program. Regulations such as EuP and Energy Star now call for minimum operating efficiency of 85 percent in power supplies for equipment such as PCs, servers, consumer products, and general-purpose AC/DC adapters and chargers.

Aside from its power-saving properties, the L6591 also provides comprehensive built-in protection such as 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 is also implemented, giving reliable operation of systems optimized for minimum no-load power.

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

-Gina Roos

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