Quasi-resonant PWM controller optimizes power adapter efficiency

The new AP3301 quasi-resonant (QR) PWM controller from Diodes Incorporated enables the implementation of high-performance, cost-effective power supplies that are capable of meeting DOE6/COC Tier 2 efficiency requirements at all load levels. Aimed at the key market of AC/DC adapters for set-top box and gaming console applications, the controller meets the auxiliary power requirements of ATX/BTX computer motherboards and is particularly suitable for use in open-frame switching power supplies. Multiple operating modes allow the AP3301 to achieve optimal efficiency at different load levels: Under low- or no-load conditions, the IC uses a burst mode to minimize 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 foldback 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 for optimum conversion efficiency. A built-in frequency dithering function helps reduce EMI emission in both CCM and QR modes. The AP3301 provides comprehensive protection features for enhanced system reliability. These 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. With just minor changes to external components, the SOT-26 packaged AP3301 provides a pin-compatible replacement solution for the company's existing AP3105/AP3125 PWM controllers.