The following note describes some of the features, benefits and applications of the FMMT617 NPN and FMMT717 PNP SOT23 transistors developed by Zetex. These devices extend the FMMT620 and FMMT720 high performance surface mount bipolar ranges. Specially optimised for the stringent requirements of battery powered systems, these tiny SOT23 packaged devices will replace much larger bipolar and MOSFET transistors, leading to significant savings in component costs and PCB sizes. Indeed the FMMT617 and FMMT717 transistors outperform many SOT223 and SOT89 types plus all SOT23 transistors presently available world-wide in terms of current handling and low losses.

The FMMT617 is a 15V NPN transistor capable of switching loads of up to 3A continuous, 12A peak. Designed to give a high mid-band gain of 450, the matrix chip geometry ensures this level of performance is maintained well above the 3A rating. For example, it’s typical hFE at 5A is still around 240 and even at 12A the hFE is a creditable 80, thus allowing the devices to handle very high current pulses, and tolerate switching transients. Giving a saturation voltage of only 150mV at 3A for a forced gain of 60, the FMMT617 is a highly efficient switch.

Read & download: http://www.zetex.com/3.0/appnotes/apps/an15.pdf

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