Power Electronics

Active Clamp Soft-Switching PWM Controllers

Texas Instruments’ four new pulse-width modulation (PWM) controllers significantly simplify implementation of active clamp/reset topologies for high-efficiency switching power supplies. The peak current-mode controllers increase efficiency in off-line power supplies and dc-dc converters used in high-end desktops, servers, 48-V telecommunications, data communications and 42-V automotive systems.

Ideal for active-clamp forward or flyback converters, TI's new UCC2891, UCC2892, UCC2893 and UCC2894 devices include an auxiliary active clamp output driver for efficient single-ended transformer reset. The controllers reduce switching losses of the converters by simply programming critical delays to achieve proper active clamp operation and deliver zero-voltage switching (ZVS) to the primary side MOSFET switches. Soft switching allows the devices to achieve higher efficiencies at high operating frequencies, and increase reliability of the overall system by lowering electro-magnetic interference (EMI) and radio-frequency interference (RFI), and reducing power supply component losses.

Building upon the success of TI's first generation UCC3580 active-clamp controller, the four new controllers improve performance while eliminating many external components. The devices include an internal programmable slope compensation circuit, a precise maximum duty cycle limit and a 1-MHz synchronizable oscillator with an internal timing capacitor. For added performance and functionality, the devices feature programmable soft-start and shutdown functionality, and an accurate line monitoring function that can program a converter's on and off transitions when determining bulk input voltage levels. The UCC2891 and UCC2893 also offer a 110-V start-up feature that removes the need of an external trickle charge bootstrap resistor to provide significant cost savings.

For more information, visit www.ti.com.

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