STMicroelectronics has announced a current-mode primary controller IC designed to build single-ended switching power converters. The L6668 has an 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 connected to the RUN or PFC_OK pins of the ST’s 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.

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 efficiency 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.

Available in production volumes now, US pricing for the L6668 is $0.40 in quantities of either 1000 or 2500 for tape-and-reel.