The timed two voltage circuit can start and run a small dc motor or solenoid. The input voltage to the LM317 three-terminal regulator ranges from 5 to 40 V, and the output voltage can range from 2 to 36 V. With input voltage Vin initially applied to the input, and capacitor C1 in a discharged state,

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The LM393 comparator's open-collector output circuit is open-circuited. Then the higher start-up output voltage is:

Vout=1.25[1 + (R3/240)]

At a time t after start-up, when:

t = -R1C1Ln[R4/(R4+R5)]

or

t = -R1C1, if R5 = 1.72 R4

the comparator output decreases. At that time, the output voltage switches to a lower value to run the device at its proper operating level.