STMicroelectronics STCH03 offline pulse-width modulation controller

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STMicroelectronics’ STCH03 offline pulse-width modulation (PWM) controller combines high integration with correct constant-current output using primary-side regulation, enabling economical mobile chargers, power adapters and auxiliary supplies to meet stringent eco-design limits for average efficiency and standby power.

At heavy loads, the product maximises efficiency by operating in quasi-resonant mode with zero-voltage switching (ZVS) controlled by detecting transformer demagnetisation. The detection circuitry also provides for line-voltage feed-forward control, which ensures constant-current regulation. Maintaining operation at the boundary of continuous (CCM) and discontinuous (DCM) transformer current, the unit limits the converter’s maximum operating frequency to 167 kHz depending on line/load conditions, and implements valley-skipping for best efficiency as the load reduces.

Energy-saving features including zero-power high-voltage start-up circuitry, as well as low quiescent current and burst-mode switching when the load is very low or disconnected, keep standby power below 10 mW to help chargers and adapters meet tough legislation. Low peak current eliminates audible noise at light load or no load, and the product features an innovative adaptive under-voltage lockout (UVLO) to ensure consistent operation at low values of transformer auxiliary bias voltage.

The product eliminates output-current sensing components, thereby reducing the charger bill of materials (BOM). The integrated start-up circuitry, which consumes zero power when inactive, also saves external components.

Other features include overtemperature and overvoltage protection (OTP, OVP) with auto-restart or optional latching operation in the STCH03L variant. In addition, soft-start prevents high peak currents at start-up and output undervoltage protection lets the device operate safely in case of an output short-circuit or low output voltage under constant-current control.

For more information: www.st.com/stch03.