within needs 2 mA which is negligible relative to the
current draw of the motor, which in the fan ranges from
about 180 mA on low to 350 mA on high (with new
The LCA717 has the advantage (for some
applications) of using a separate power source for the
load, which is the way the circuit schematic here is shown.
In this fan application, both the timer and the load share
the same two series-connected D cell batteries. Figure 12
shows the completed circuit board, which was easy to fit
in the cavity of the fan base.
I hope this short article will serve as an indication of
the capabilities of this relatively new timer. The documents
that CSS has prepared for these chips give much more
information. They are very thorough, easy to follow, and
have plenty of illustrations — some of which have been
presented here (with permission of course!). The
information sheets available for downloading from the CSS
website include SPICE models, timer delay and adjustable
duty cycle calculators, and a collection of application
circuits showing the many ways this remarkable timer can
be put to work. NV
February 2016 37
FIGURE 12. Circuit board of the now battery-saving fan.
FIGURE 11. Schematic of the one-shot circuit used for
controlling the fan motor. Note the bypass capacitor
across the supply and ground; 0.1 μF suffices in such
FIGURE 10. The “O2Cool” personal fan powered by two
D cell batteries.
FIGURE 9. Screenshot of the computer-based CSS555