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Product Newsletter
Smart PWM controller from STMicroelectronics increases efficiency and reduces costs for notebook power supplies
STMicroelectronics a world leader in power ICs, has announced an innovative current-mode primary controller IC designed to build sin-gle-ended switching power converters.
The L6668’s advanced functions make it one of the most innovative and efficient controllers available for power supplies.
Ideally suited for use in high-end AC/DC adapters and chargers for notebook or laptop PCs, the versatility of the L6668 current-mode PWM controller also makes it suitable for power supplies of set-top boxes, DVD players, low-end LCD TVs and other digital consumer equipment. In addition, excellent energy-saving features make the IC a good choice in low-power auxiliary converters used in high-end LCD and plasma-based TVs, desktop PCs and server power supplies.
The IC combines a number of functions able to change the way the device works to optimize power processing under all operating conditions with excellent electrical characteristics. This combination allows development of robust and energy-efficient designs.
One of these innovative functions is the interface with the PFC controller that enables pre-regulator turn off when the load level falls below a threshold, saving typically 0.5 to 1W of no-load power consumption. This interface can be easily connected to the RUN or PFC_OK pins of the ST’s advanced L6563 Power Factor Corrector IC.
In addition, the chip’s high-voltage (HV) technology, when combined with a multi-chip approach, makes it possible to integrate a high-voltage start-up system that is connected directly to the rectified mains voltage. The HV generator is physically located on a separate chip, made with BCD (Bipolar-CMOS-DMOS) off-line technology able to withstand 700V, controlled by a low-voltage chip, where all of the control functions reside. This feature, in addition to burst-mode operation and the very low quiescent current, helps it to be compliant with energy saving recommendations with minimum usage of external components. Cost and space saving can be minimized with no compromise on performance.
The L6668 achieves its high level of efficiency by operating in three different modes, depending on the load conditions. At heavy load, the IC drives the converter at a programmable fixed frequency to optimize its size and weight. Then, if the load is reduced below a threshold, the switching frequency is adapted to minimize conversion losses. Additionally, the improved Standby function causes a smooth frequency reduction as the load is progressively reduced. Eventually, at very light load the device enters a special operating mode (burst-mode with fixed, externally programmed peak current) that brings the switching frequency to extremely low values, hence essentially zeroing all losses related to switching. Optimum size/efficiency trade-off can be achieved and conversion efficiency is maximized under all loading conditions, in addition to the on-board high-voltage start-up. All this means high ef-ficiency benefits with low dissipation on a light load.
The L6668 also includes programmable soft-start, slope compensation for stable operation at duty cycles greater then 50%, a disable function, current sense leading edge blanking to improve noise immunity, latched disable for over-voltage or over-temperature shutdown, and protective output current limiting in case the secondary diode fails to short circuit.
The new power supply controller is Blue Angel, Energy Star and EU Code of Conduct compliant, and is available now in an SO16 package.
For more
information on the full range of STMicroelectronics products available
from Anglia please call +44 (0)1945 474747 or email info@anglia.com
