hot to the touch, even with a small heat sink attached. This was
too hot for a closed plastic shell. A melt-down was coming.
Fortunately, there is relatively new technology in the form
of switching regulators to save the day. I had on hand a few
78ST105HC modules which come in a plastic frame with
no heat sink. They provided the same regulation function
and worked great, generating little heat if any. While the
78ST105HC is hard to get, their success prompted me to find
the PSU2-5 from EzSBC.com, also available from their eBay
store, an even smaller switching regulator in the same package
outline as an LM7805. The heat problem was solved. A small
capacitor was added across the output of the regulator —
about 33uf at 25 volts. This capacitance value is not critical but
use at least a 10 volt rating.
The last component in the basic power unit is a magnetic
reed switch to turn the unit on and off. A plain single-pole
6
6. LiPo batteries.
Battery-powered models - 4
MRH-Nov 2014
