BS250p Polarity Protection and Correction
I chose this method for the HB2 to take advantage of its very low voltage drop. However, I made a mistake in the layout-
the transistor orientation is shown incorrectly. Q15 must be flipped around to take full advantage of the BS250p. It will still
work the incorrect way but the transistor itself can be damaged by reverse polarity if left in its incorrect orientation (I finally
realized this when I fried my own transistor when I plugged the power in backwards).
Flip Q15 so that the half-rounded side faces up instead of down. The BS250p is slightly flatter than the typical T0-92 tran
-
sistor casing. Use this guide:
In the corrected version, the “BS250p” marking on the transistor casing faces the red arrow.
DC Jack
The placement of the two NSL-32 devices is not really optimal in terms of overall design, but it’s what worked with this
PCB layout. If possible, one of the external nut jacks (
http://smallbear-electronics.mybigcommerce.com/2-1-mm-plastic-
round-external-nut/
) would be best. But, if you are like me and don’t have those the typical jack will work fine. To make
the internal nut jack work I cut the Ring tab off (it isn’t needed anyway) and gently bent the tab outward. This posed no
problems.
Notes
