Provides line voltage feed-forward control
Soft-start function prevents high peak current during startup

STMicroelectronics (ST) has launched the STCH03, an offline Pulse-Width Modulation (PWM) controller that provides both accurate constant current output and high integration using primary-side regulation. This controller enables economical mobile chargers, power adapters, and auxiliary power supplies to meet stringent eco-friendly design constraints in average efficiency and standby power.

STCH03 can maximize efficiency even at higher loads by operating in a ZVS (Zero-Voltage Switching) quasi-resonant mode controlled by transformer demagnetization detection. In addition, this detection circuit provides line voltage feed-forward control to ensure accurate constant current regulation.

STCH03 maintains operation within the boundaries of continuous (CCM) and discontinuous (DCM) transformer currents, limits the converter's maximum operating frequency to 167 kHz depending on line and load conditions, and implements Valley-Skipping to achieve optimal efficiency when the load is reduced.

When the load is very low or disconnected, energy-saving features such as low standby current and burst-mode switching, as well as zero-power high-voltage start circuits, allow standby power to be kept below 10mW, enabling compliance with stringent regulations such as the CoC Tier 2 power supply efficiency specifications planned for introduction in chargers and adapters.

STCH03 eliminates audible noise at light or no load with low peak current and features innovative adaptive UVLO (Under-Voltage Lockout) to maintain consistent operation at low transformer auxiliary bias voltage values.

The STCH03, which offers the advantages of precise primary-side constant current regulation, can reduce material costs for the charger because it eliminates the need for output current sensing components. Additionally, it integrates a startup circuit that consumes zero power when inactive, allowing for the reduction of external components.

STCH03 is equipped with more features that can reduce external component and material costs, including over-temperature protection (OTP) and over-voltage protection (OVP) that support automatic restart or optional latching operation provided in STCH03L. In addition, the soft-start function can prevent high peak current during startup, and the under-voltage protection (UVP) function allows the device to operate safely even if the output is short-circuited or the output voltage is low during constant current control.