Flyback Converter Controller from STMicroelectronics Supports Both Fixed Frequency and Quasi-Resonant Operatin

Flyback Converter Controller from STMicroelectronics Supports Both Fixed Frequency and Quasi-Resonant Operating Modes

Cost-saving multi-mode controller also integrates input/output protection, PFC interface and adaptive UVLO in single chip

STMicroelectronics announced a flexible and cost-saving new controller for high-performance flyback power converters, which can operate in either the Fixed‑Frequency (FF) or the Quasi-Resonant (QR) mode – the two principal operating modes used in flyback SMPS – selectable by connection of a single pin – thereby enabling manufacturers to stock and qualify a single component to meet the requirements of different applications. In addition, the chip integrates many protection capabilities commonly implemented with external components, and energy-saving features that help the designer to meet the most severe energy regulations.

The L6566 selectable multi-mode controller is suitable in applications such as flyback AC/DC adapters, TV and LCD monitors, small size LCD TVs, high end chargers, and in other consumer equipment such as DVD players and set-top boxes.

Under very light load conditions, in both operating modes, the chip enters a controlled burst-mode state at low frequency (a few hundred Hertz) with constant peak current, in order to minimize total power requirements and to comply with world-wide energy saving recommendations. The controller’s quiescent current (less than 3mA) and on-board non-dissipative start-up circuit – a product of ST’s high-voltage process technology – further improve the overall efficiency.

The IC is available in two orderable versions, L6566A and L6566B. The L6566A is designed specifically for converters supplied through a front-end Power Factor Corrector (PFC) circuit; it provides an interface to the PFC to turn off the regulator under light or no-load conditions and during all the fault conditions. The L6566B version is intended for applications where a front-end PFC is not used, and it includes an oscillator frequency modulation input to reduce EMI (electromagnetic interference) emissions, saving cost and size of the line filter when FF operation is selected.

On-chip input/output protection features include over-voltage (OVP), cycle by cycle over-current (OCP) and over-temperature protection (OTP), brownout protection, and inductor saturation detection (hi-cap mode OCP). An innovative adaptive under voltage lock out (UVLO) circuit prevents the possibility of intermittent operation which can occur under no- load conditions due to the possible IC’s own supply voltage fluctuations caused by the transformer’s parasitics. This high level of integration enables designers to reduce the number of external components, minimizing PCB area, reducing costs and increasing the reliability of the power supply.

The L6566 is available in volume now, in an SO-16 package, priced at $0.50 in quantities of 2500 pieces. ■