STMicroelectronics’ SRK1004 synchronous-rectifier controllers save space and increase efficiency in the secondary side of active-clamp, resonant, and quasi-resonant flyback (ACF, AHB, QR) converters for chargers, power adapters, and switched-mode power supplies. The minuscule 2 x 2mm ICs supersede the SRK1001 and implement a new switch-off algorithm for increased efficiency and robustness.
With six variants available, the SRK1004 series lets designers choose logic-level or standard MOSFET gate drive, and 25 or 150ns turn-off delay to compensate for drain inductance. Suitable for active clamp, resonant and quasi-resonant flyback topologies, the controllers also contain circuitry that creates a turn-on window to prevent unwanted switching. The output can sink up to 1.6A and source 0.6A to the gate, while the switching frequency of 500kHz permits a compact and low-cost design.
Leveraging ST’s robust silicon-on-insulator (SOI) process, the SRK1004 can control the MOSFET in either low-side or high-side connection with up to 190V drain-source voltage. With a wide supply-voltage range, from 4 to 36V, the IC can be powered from the converter’s output in a low-side configuration or from the transformer in a high-side configuration. This lets designers avoid providing a dedicated auxiliary power supply and so minimise the bill of materials. The SRK1004 contains a linear regulator that supplies the IC’s internal circuitry and gate driver as well as providing power at an output pin for off-chip circuitry.
Six individual evaluation boards, EVLSRK1004A-F, are available to help quickly start new projects and identify the SRK1004 variant best suited to the converter circuit and MOSFET.
