36W USB charger based on STCH03L and SRK1000B with selectable output voltage (5-9-12 V @ 3A)

The power circuit is a quasi-resonant (QR) flyback converter, with peak current mode control, based on the STCH03L IC. The circuit operates with secondary side constant voltage (CV) regulation through an optocoupler and is capable of providing constant output current (CC) regulation using primary sensing feedback.
The STCH03L embeds a 650 V, non-dissipative, HV startup cell, which, along with the extremely low quiescent current and burst-mode management, helps minimize residual input consumption, thus achieving less than 20 mW under no-load condition.
At secondary side, the SRK1000B controller implements synchronous rectification to increase system efficiency: it controls the synchronous rectifier MOSFET, driving its gate with minimal turn-on delay and maximizing the turn-off time instant (through an adaptive mechanism) so that the residual conduction of the SR MOSFET body diode after turn-off reduces to the target value of 300 ns.
The charger is designed to meet the most stringent energy saving recommendations (Eu CoC rev. 5 - Tier 2 and EPS of DOE USA) as well as EMI regulation EN55022-Class-B for line conducted noise emissions.