With the introduction of its new 'Breakthrough In Small-Signal' switching transistors, Philips Semiconductors, the largest European semiconductor manufacturer, adds the benefits of extremely low collector-emitter saturation voltage to the inherently low turn-on voltage of bipolar transistors, giving designers the advantage of reduced power dissipation in low-voltage battery-powered equipment such as mobile phones and pocket pagers.

"For switching low-voltage loads at peak currents up to one or two amps, silicon bipolar transistors still remain the favoured device for many design engineers because of their lower turn-on voltage and better peak current handling capabilities compared to MOSFETs," said product marketing manager Andreas Niemann. "Our new Breakthrough In Small-Signal transistors mean significantly lower power dissipation in the switching transistor, resulting in considerably longer battery life for mobile equipment."

To achieve typical V_CE(sat) figures as low as 0.25 V and DC current gains of over 200 for SOT23 packaged versions operating at a collector current of 1 A, Philips Semiconductors developed an innovative emitter structure for these new transistors that reduces the bulk emitter resistance. In addition to reducing power dissipation by keeping the emitter resistance low, Breakthrough In Small-Signal transistors have also been designed to maintain their performance at high junction temperatures. These two features allow the SOT23 packaged versions (the npn PMMT491A and pnp PMMT591A) to handle continuous load currents as high as 1 A - twice the load current capability of conventional SOT23 transistors. It also means that in many applications these transistors can be operated without any additional heatsinking.

This is a staggering breakthrough in one's thinking about the plain old transistor. It puts the bipolar in line with MOSFETs in terms of the ability to handle power for a given package size while also taking advantage of the bipolar's inherently better current handling, high current gains and the lower turn-on voltage. It may seem like small change but this is what innovation is all about; these parts and the future developments from this technology are going to represent extremely high volume business for Philips.

With the 5-A capability of the BDL31 and BDL32 there is the potential of finding tens of millions of existing sockets that have been designed at a lower price and without heatsinking in many cases; there should also be very considerable design-in business quickly afterwards. The 1- to 2-A business that these parts might grab is totally immeasurable.