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Power supply controller enables energy-efficient designs

Posted: 11 Oct 2007 ?? ?Print Version ?Bookmark and Share

Keywords:mixed-signal controller IC? embedded power supplies? power transistors?

Fabless startup Cambridge Semiconductor Ltd has unveiled details of its first product, a mixed-signal controller IC for switched-mode power supplies that it expects will help companies produce much more energy-efficient equipment.

However, the company has opted not to integrate the control circuitry with power transistors, the capability the company was founded to exploit in August 2000 and subsequently branded as its PowerBrane technology.

"We are continuing to develop the PowerBrane technology and we see it as part of the long-term value of the business," David Baillie, CEO of CamSemi, told EE Times. He added: "We have demoed it and we can provide parts but it's not a product."

Energy-saving device
Baillie said that when the company approached early-adopter customers the demand for the control technology persuaded the company to bring it to market in advance of other product developments.

As a result, C2470 series of controllers is already in volume production. The parts are being deployed within a resonant single-switch, feed-forward power supply topology, an architecture CamSemi claimed has never been applied in an integrated form for off-line AC/DC power conversion.

This use of SMPS for the 6-40W range should allow manufacturers of chargers, adapters and embedded power supplies to achieve operating efficiencies in excess of 80 percent and 100mW standby power consumption, CamSemi said.

"We are three times less inefficient than linear power supplies," said Baillie, pointing out that power supply inefficiency means trillions of kilowatt-hours of energy are wasted each year.

The resonant design with zero voltage at switching minimizes losses and allows a low-cost discrete bipolar transistor to be used. Such transistors are usually about a third of the cost of comparable MOSFETs, said John Miller, VP of business development at CamSemi.

Other details
The C2470 series parts are manufactured in a standard 0.35?M mixed-signal CMOS process and are used to monitor current flow and switching frequency and to provide PID [proportional, integral, differential] control of the base of the power transistor. The digital device also allows the power supply to switch between modes of operation and provide protection against excursions outside the transistor's safe operating area.

Baillie declined to name the manufacturer of its circuits or say how soon CamSemi would begin offering a design with integrated power transistors.

Given initiatives such as Energy Star and the California Energy Commission, manufacturers are under increasing market and legislative pressures to stop producing bulky and energy-inefficient linear transformers. However, manufacturers' only option to date has been to migrate to much more costly and complex SMPS flyback or ringing choke converter (RCC) designs, CamSemi said.

"Our goal is to enable energy-efficient offline power conversion without a cost penalty and the C2470 family of controllers does just that. The devices have been specifically optimized for high volume, low cost, single rail input markets while offering double the efficiency over traditional linear supplies," said Baillie.

Because of the zero switching the devices are able to use relatively low frequency SMPS, typically 50kHz to 100kHz, with the additional advantage of a low EMI signature without having to design-in complex EMI filtering circuitry typically needed with SMPS, Miller.

The first three members from the C2470 family are available in volume for applications such as battery chargers, mini adapters, routers, cordless phones and audio systems. Indicative pricing for C2472PX2, the SO23-6 part, is 45 cents each for 1,000-piece quantities.

- Peter Clarke
EE Times Europe

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