Boosts Efficiency, Economy, and Stability of Ultra-Low Standby Power Supplies
Geneva, July 2, 2018 — STMicroelectronics’ STCH03 offline Pulse-Width Modulation (PWM) controller combines high integration with accurate constant-current output using primary-side regulation enabling economical mobile chargers, power adapters, or auxiliary supplies to meet stringent eco-design limits for average efficiency and standby power.
At heavier loads, the STCH03 maximizes efficiency by operating in quasi-resonant mode with zero-voltage switching (ZVS) controlled by detecting transformer demagnetization. The detection circuitry also provides for line-voltage feed-forward control, which ensures accurate constant-current regulation. Maintaining operation at the boundary of continuous (CCM) and discontinuous (DCM) transformer current, the STCH03 limits the converter’s maximum operating frequency to 167kHz depending on line/load conditions, and implements valley-skipping for best efficiency as the load reduces.
Energy-saving features including zero-power high-voltage startup circuitry, as well as low quiescent current and burst-mode switching when the load is very low or disconnected, keep standby power below 10mW to help chargers and adapters meet tough legislation such as the incoming CoC Tier 2 power supply efficiency specifications. Low peak current eliminates audible noise at light load or no load, and the STCH03 features an innovative adaptive under-voltage lockout (UVLO) to ensure consistent operation at low values of transformer auxiliary bias voltage.
With the advantage of accurate primary-side constant-current regulation, the STCH03 eliminates output-current sensing components, thereby reducing the charger bill of materials (BOM). The integrated startup circuitry, which consumes zero power when inactive, also saves external components.
The STCH03 contains many more features to help save external components and BOM cost, including over-temperature and over-voltage protection (OTP, OVP) with auto-restart or optional latching operation in the STCH03L variant. In addition, soft-start prevents high peak currents at startup, and output under-voltage protection lets the device operate safely in case of an output short-circuit or low output voltage under constant-current control.