Synchronous-rectification controllers replace conventional diode rectification with a synchronous-rectification MOSFET, using digital adaptive algorithms to dynamically adjust switching timing across multiple operating modes, reducing rectification loss and raising power-supply efficiency. Diode rectification carries an inherent forward-voltage-drop loss, and replacing it hinges on precisely detecting the moment current crosses zero and reverses — get the timing wrong and the gain shrinks, or reverse current flows back and damages the device. Timing precision and adaptive capability are the core value of this chip class.
Reading the Key Parameters
- Supported operating modes (op_mode): Catalog parts are generally marked as supporting CCM/QR/DCM, automatically matching rectification timing as load swings from full to light. Wider mode coverage fits a broader range of applications.
- Turn-on / pre-off thresholds (turn_on_th_mv / pre_off_th_mv): Catalog turn-on thresholds cluster around −150~−180mV (turn-on triggers once drain-source voltage drops below this value), and pre-off thresholds cluster around −50~−52mV (turning off ahead of the zero-crossing to prevent reverse current). These settings directly shape loss reduction and light-load safety margin.
- Minimum turn-on / turn-off time (min_turn_on_us / min_turn_off_us): Catalog turn-on floors span 0.5~1.0μs and turn-off floors span 0.2~2.5μs — smaller values suit higher switching frequencies or light-load discontinuous conduction.
- Package: Catalog parts all use the compact SOT23-6L package, suited to placing the controller close to the secondary-side SR MOSFET and shortening drive-loop parasitic inductance.
Three Steps to Select
- Confirm the operating modes that need to be covered, based on target topology and actual load range.
- Check that turn-on/pre-off thresholds match the external SR MOSFET's drain-source characteristics, and evaluate open-loop protection under light/no load.
- Check minimum turn-on/turn-off time against the target maximum switching frequency to confirm response speed keeps up.
Common Pitfalls
- Selecting a part for being labeled "multi-mode" without checking whether its thresholds match the target MOSFET's actual characteristics.
- Overlooking open-loop and reverse-current protection under light/no-load conditions, only discovering the issue at test.
To cross-compare parts by operating mode, threshold parameters, package and other parameters, use our online selection tool, or contact us for part-selection support.