STMicroelectronics introduced three new bipolar power transistors specifically designed for use in electronic transformer circuits for lighting applications, where the main requirement is the ability to withstand the very high currents that flow during lamp turn or short circuits. Known as the BUL39D, BUL49D and BUL59, the new devices feature increased ruggedness, giving greater safety margins when operating in these conditions, and a guaranteed wide Reverse Bias Safe Operating Area with a VCEW.capability up to 450V at high current levels.

Key specifications of the BUL39D, BUL49D and BUL59 include maximum collector currents of 4, 5 and 8A, respectively, maximum power handling capability of 70, 80 and 90W, respectively, and V_CES /V_CEV of 850V. The BUL39D and BUL49D also include an intrinsic free-wheeling diode.

What can you say but "wow!" What is most impressive about the specifications of these bipolars is the part-to-part control of the switching times. You can design a device that will take the rigorous changes in current but if they are being used in pairs -- which they often will be -- they must switch together, otherwise the small differentials in the crossover will extend towards twice the peak currents allowed for just one device.