Transistors increase power supply power density

13th August 2007

ES Admin

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Zetex Semiconductors has introduced a series of miniature NPN and PNP transistors for MOSFET gate driving in latest generation power supplies. The first bipolars to be provided in the SOT23FF package, with a footprint of 2.5mm x 3mm and an off-board height of just 1mm, the ZXTN and ZXTP transistors offer a lower saturation voltage and higher current gain hold up, leading to improved circuit efficiency and cooler running.

Covering the operating voltage range from 20V through to 100V the Zetex bipolar transistors are able to drive MOSFET gates faster and more efficiently than CMOS IC alternatives and being immune to latch-up, they offer an improvement in overall system reliability. The use of the SOT23FF package also allows the devices to sit as close as possible to the MOSFET, helping to minimise track inductance and ringing effects.

The 20V ZXTN19020CFF and ZXTP19020CFF have guaranteed gains of 100 at 7A and 110 at 5A respectively. When connected in a common emitter configuration they provide extremely fast switching, with propagation times less than 2ns and rise and fall times between 10 and 20nsecs. With a peak current performance up to 15A, they offer a highly cost effective alternative to dedicated gate driver ICs.

In saturated switch applications based on the Royer and push pull topologies used in POL DC-DC modules and emergency lighting, the transistors’ low saturation voltage capability provides a significant advantage. As an illustration, the 60V rated ZXTN19060CFF NPN has a saturation voltage of just 150mV at 1A with a base drive of 10mA, or 135mV at 2A and a base drive of 40mA.