Quasi-Resonant PWM Controller Optimizes Efficiency
The AP3301 quasi-resonant (QR) pwm controller introduced by 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. Targeting the key market of ac-dc adapters for set-top box and gaming console applications, this 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 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 Diodes’ existing AP3105/AP3125 PWM controllers. The AP3301 is priced at $0.20 each in quantities of 1k units.
