Novel convertor chip raises PSU efficiency

The STR-T4000 is a partial resonant convertor integrated circuit optimised for use in power supplies for IT-related equipment and flat panel displays.

The new STR-T4000, developed by Sanken Electric and available in Europe from Allegro MicroSystems Europe, is a partial resonant convertor integrated circuit optimised for use in power supplies for IT-related equipment and flat panel displays.

The new device combines small size, low cost, high efficiency and low standby power loss to meet the latest energy-saving and antipollution requirements of microprocessor controlled digital systems operating in the 1.5V supply voltage range.

The partial resonant convertor uses a new circuit topology which allows it to handle anything from zero load condition in standby mode to 300 W of output power as encountered in IT-related equipment and flat-panel TV applications.

The power control IC automatically adjusts its operating mode to the load conditions, and features automatic dead-time setting.

It uses Sanken's patented BCD (bipolar, CMOS and DMOS) process to achieve a 900V breakdown voltage.

This multimode power control IC is designed for use with a new design of multipath transformer, also developed by Sanken.

The new compact multipath transformer provides the partial resonance by using core saturation, along with low ripple current to the output capacitor.

Crossregulation is only +/-3% at 5-100% load ratio, and the voltage/turns ratio of the transformer is half that required for a normal flyback convertor.

The resulting improvement in secondary output accuracy means that the requirement for additional discrete regulator components is eliminated.

Moreover, the reduction in ripple current means that the output capacitor need only be one-fifth of the value of that required for a flyback convertor.

Together, the STR-T4000 and the multipath transformer form the basis of a 300W switch-mode power supply that provides the benefits of low standby power, system downsizing, a minimal component count, high efficiency, low noise and a multi-output capability.

Typical improvements include a cost reduction of more than 30%, a 30% smaller footprint, and a 20% reduction in power loss.

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