Quasi-resonant PWM controller boosts efficiency in power adapters
13 October 2016 
They enable the implementation DOE6/COC Tier 2 efficiency requirements at all load levels, in AC/DC adapters for set-top box and gaming console applications. The controller also meets the auxiliary power requirements of ATX/BTX computer motherboards and is suited for use in open-frame switching power supplies.
Multiple operating modes allow the controller to achieve optimal efficiency at different load levels. Under low- or no-load conditions, the IC uses a burst mode to minimise standby power consumption while operating at a minimum switching frequency of approximately 20kHz to avoid audible noise.
At intermediate loads, a valley-lock QR mode with frequency fold-back improves efficiency and EMI performance. For heavy loads, or under low-line input conditions, the controller enters a continuous conduction mode (CCM) at a fixed 62kHz switching frequency. A built-in frequency dithering function helps reduce EMI emission in both CCM and QR modes.
Protection features include AC-input brown-out protection, cycle-by-cycle current limit, precise output over-voltage protection, internal over-temperature protection, overload protection, and a pin fault‑protection circuit, which detects floating or short connections on key signal pins and disables PWM switching to protect the power system.