Power adapter controller ICs cut parts count and cost

EDN Europe, 27 Nov 2008

CamSemi (Cambridge Semiconductor) has announced new devices that employ primary-side-sensing for output voltage and current regulation in wall-adapter power supplies for chargers and low-power consumer products. The C2140 series offers current and voltage regulation of +/- 5% and targets high volume, universal input applications rated up to 8 W. The parts also feature programmable cable compensation and switching frequency adjustment to enable greater design and manufacturing flexibility. Designers can cut component count, while developing more reliable and lower-cost designs to meet Energy Star 2.0, European code of conduct and other worldwide energy-efficiency regulations. The C2141PX2 and C2142PX2 parts are rated at 4 W and 8 W respectively, packaged in SOT23-6 and are available in volume now. The C2140 family eliminates the need for optocouplers and all secondary-side feedback circuitry, as well as any additional components that designers may need to specify to improve the current regulation from a typical PSS flyback design. The controllers use patented algorithms combined with digital techniques to more accurately monitor the output voltage and provide tighter current regulation than has previously been possible. This approach enables quasi-zero-voltage switching, which drives up operating efficiencies and delivers improved current regulation to maintain the optimum lifetime of lithium ion batteries.

The new devices include programmable cable compensation of up to 10% to give tight voltage regulation at the end of the cable, while helping to minimise the copper content (and therefore cost) of the cable. The compensation is fully adjustable in the design phase allowing one standard design to be quickly modified to accommodate different cable lengths or gauges. The controllers can also be easily adapted to match the required switching frequency of the end application by simply specifying one external component. The controllers are designed for use with low-cost bipolar transistors and have protection features such as over-temperature, input over-voltage and output short-circuit included as standard to further simplify designs and reduce system costs.