Dual operating modes boost controller flexibility

The L6566 selectable multimode controller is suitable for applications such as flyback AC/DC adapters, TV and LCD monitors, small size LCD TVs, high end chargers and other consumer equipment.

STMicroelectronics has released a flexible controller for high-performance flyback power convertors, which can operate in either the fixed-frequency (FF) or the quasi-resonant (QR) mode, the two principal operating modes used in flyback SMPS.

The mode is selected with connection of a single pin, 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 multimode controller is suitable for applications such as flyback AC/DC adapters, TV and LCD monitors, small size LCD TVs, high end chargers and 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 minimise total power use.

The controller's quiescent current (less than 3mA) and on-board nondissipative start-up circuit further improve the overall efficiency.

The IC is available in two versions, L6566A and L6566B.

The L6566A is designed specifically for convertors 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, reducing costs and the 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 adaptive under voltage lock out (UVLO) circuit prevents the 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, minimising PCB area, reducing costs and increasing the reliability of the power supply.

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