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ST's new Hybrid BJT/MOSFETs deliver speed and power

Posted: 14 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:stmicroelectronics? emitter-switched bipolar transistor? ebst? single-ended primary inductance converter? sepic?

Touting a breakthrough in high-voltage, high-switching applications, STMicroelectronics' new hybrid emitter-switched bipolar transistors (EBST), particularly suited to industrial three-phase auxiliary power supplies and single-ended primary inductance converters (SEPIC), boasts the industry's best combination of low forward voltage drop, high blocking voltage, and fast switching speed.

The stc03de170, stc05de150 and stc08de150 are intended to resolve the power supply designer's dilemma of choosing either the bipolar junction transistor (BJT, low conduction losses but slow switching speeds) or the MOSFET (fast switching but high conduction losses).

The combination BJT and MOSFET devices, connected in cascode, deliver comparable performance to single BJTs working at switching frequencies at 130kHz under hard (snubberless) switching conditions, which the devices safely handle thanks to their square reverse bias safe operating area (RBSOA). Other features include high voltage capability (up to 1.7kV), which allows designs to operate with a higher flyback voltage and, consequently, a higher duty cycle. This, in turn, allows the power supply to handle higher power or to operate within a wider range of input voltage.

In addition to their high breakdown voltage (1.7-, 1.5- and 1.5kV, respectively), these devices have a low on-resistances (0.55-, 0.17- and 0.11 ohms, respectively). In comparison, the traditional 1,500V power MOSFET typically exhibits an on-resistances in the range of 5 ohms to 9 ohms.

All three devices feature a Vcs(sat) value of 0.9V, thus minimizing conduction losses, while the absence of tail currents also cuts turn-off losses. Thus the devices run cooler and are more reliable for applications in the 30-150 watt range, according to the company.

The STC03DE170, STC05DE150 and STC08DE150 are housed in a custom-designed four-lead TO-247 package featuring a lateral collector pin to increase the clearance between high voltage and low voltage pins. These products are available in production volumes, with pricing for sample (100-piece) quantities of $3.10, $3.30 and $3.60 each, respectively. The company provides comprehensive support for the new devices, including application notes and reference design boards.

-Vince Biancomano


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