Offline pulse-width modulation controller for low standby power supplies

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

At heavier loads, the STCH03 helps maximise efficiency by operating in quasi-resonant mode with zero-voltage switching controlled by detecting transformer demagnetisation.

The detection circuitry also provides for line-voltage feed-forward control, which the company says helps ensure accurate constant-current regulation.

Maintaining operation at the boundary of continuous and discontinuous 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 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 adaptive under-voltage lockout to ensure consistent operation at low values of transformer auxiliary bias voltage.

With accurate primary-side constant-current regulation, the STCH03 eliminates output-current sensing components, thereby reducing the charger bill of materials. The integrated startup circuitry, which consumes zero power when inactive, also saves external components.

The STCH03 also features over-temperature and over-voltage protection 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.

The STCH03 is in production now, comes in the SO-8 package and is priced from $0.54 for orders of 1000 pieces.

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