Connected in this
manner, an LM317 1-A adjustable-voltage regulator can be used to control the speed of a
miniature dc motor or vary the brilliance of a small lamp. The circuit does so by
controlling the pulse width, and therefore the current, to the load device.
To set the desired maximum output voltage,
momentarily close S1 and adjust R3. Connect either a lamp or small dc motor (as is shown
in the schematic to the circuit's output) and adjust R4 for the desired results. Any
device that is driven by this circuit should have a current requirement of 1 A or less.
And you should be sure to use good-sized heatsink for the LM317 regulator IC. (Reprinted
with permission from Popular Electronics, 3/92, p. 72. Copyright Gernsback Publications,
Inc., 1992.) From figure FE63-5 of Encyclopedia of Electronic Circuits on CD-ROM
Vol. 1.
