STMicroelectronics has unveiled a controller for LLC resonant voltage converters, the L6699D, is the first of its type to combine anti-capacitive protection, auto-adaptive dead-time and enhanced safe-start operation. These features reduce stress on associated power semiconductors while enabling optimized zero-voltage switching for better energy efficiency across the power supply’s full load range.
By reducing stress on the power MOSFETs of the converter half-bridge, the L6699D’s anti-capacitive protection and safe start-up allow designers to specify smaller, lower-cost MOSFETs. There is also a patented method for improving burst-mode operation, which reduces audible noise from the converter without requiring a large or expensive filter.
ST’s patented auto-adaptive dead-time adjusts the duration when both power switches in the half-bridge are turned off. This enables optimized zero-voltage switching over the complete load range from light load to full load using a smaller transformer and resonant components, thereby minimizing both solution size and energy loses in the resonant components. By increasing efficiency at light loads, the L6699D can also save the need for a separate standby power supply in equipment such as televisions pr all-in-one PCs thereby further reducing cost and form factor.
The L6699D is used with two companion chips, the L6563H Power-Factor Correction (PFC) controller and SRK2000 synchronous rectifier driver, to create a complete control solution for medium to high-power applications. Compared to other approaches that combine resonant control, PFC control and sometimes also power MOSFETs in the same package, ST’s discrete devices enhance functionality and flexibility for designers.
The three small, low pin-count packages enable small form factors and high power density that cannot be achieved using a bulky, integrated device. The three chips are also competitively priced compared to more expensive integrated devices. The L6699D is sampling now in the SO16N package, priced at $1.50 for orders over 1000 pieces and mass production is to begin this quarter.
ST is also unveiling its first trench-gate field-stop IGBTs for use in PFC circuits, as well as other energy-conscious equipment such as solar-power inverters, welders or uninterruptible power supplies. By combining trench-gate and field-stop technologies, which reduce conduction and switching losses respectively, these devices can improve overall system energy efficiency. ST’s field-stop process also achieves high thermal performance and helps enhance safety in high-power applications using multiple devices in parallel. So far, ST has introduced two devices in its new field-stop trench-gate family; the 650V/60A STGW60H65F and 600V/50A STGW50H60DF.