Primary-side controller employs bipolar-transistor-drive scheme

June 25, 2013 // By Graham Prophet
CamSemi (Cambridge Semiconductor) has announced advances in its bipolar transistor (BJT) drive scheme and the first of a new series of Primary Side Sensing (PSS) controllers to exploit these developments.

The C2172 PSS controller will enable manufacturers to develop what the company believes will be the industry’s lowest cost, most energy-efficient BJT-based solutions for mobile phone chargers and other universal input applications rated to 6.5 W. The new drive scheme will also help designers improve the ruggedness of their designs.

CamSemi’s proprietary BJT drive technology uses combined base and emitter switching to boost switching performance and deliver higher operating efficiencies, more Reverse Bias Safe Operating Area (RBSOA) margin and the flexibility to accommodate a wide range of low cost BJTs. Competitive drive schemes control just one transistor node which can impact operating efficiency, cut the RBSOA margin and reduce design robustness unless several additional components are included to counteract this.

C2172 is the first CamSemi PSS controller to combine this powerful new drive scheme with the company’s PSS technology to deliver no-load power consumptions well below 30 mW and ‘best in class’ load-transient response but with significantly lower system cost and component counts. The IC power consumption and design have also been optimised to enable the benefit of fast start but without needing the additional cost and complexity of an additional active start-up switch. CamSemi’s next-generation PSS controller is also fully compliant with all the newly emerging standards for ‘MoU’ compliant universal USB chargers.

“CamSemi C2172 is the first of our more ’cost efficient’ second generation PSS controllers that will build on the considerable commercial success that we have achieved to date in the mobile consumer charger market. Our lead partners have already started to develop C2172-enabled designs and we expect several to be in high volume production within the next few months,” said David Baillie, CEO of CamSemi.

C2172 also incorporates many of the same design benefits as the company’s existing PSS controller families including: accurate current and voltage regulation of ±5% without board-level trimming; quasi-resonant switching to reduce EMI and to enable compliance with efficiency standards with