US 4,774,444 AGranted

Speed control circuit for an electric motor

OwnerPaul H. Wernerinventor

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Abstract

A speed motor control circuit for an electric motor of the type which drives a louvered sign assembly between predetermined rotational positions. The speed control includes a silicon controlled rectifier which is connected in series between the motor and the power supply. A unijunction transistor has one of its bases connected to the gate of the silicon controlled rectifier to switch on, or activate, the silicon controlled rectifier whenever the unijunction transistor becomes conductive. A variable resistor controls the bias to the emitter for the unijunction transistor in order to vary the time period or duty cycle that the unijunction transistor conducts and thus the time period or duty cycle that the silicon controlled rectifier is in its conductive state. A switch assembly and timing module are also employed to activate the motor at predetermined time intervals and for a predetermined angular rotation of the motor shaft.

Claims5

Dependent claims

A speed control circuit for an electric motor having an output shaft, an inoput terminal and an output terminal which, when connected to different voltage levels, rotatably drives the motor shaft,

a voltage source having two voltage levels,
a silicon controlled rectifier having a gate, cathode and an anode, said anode being connected to said output terminal, said cathode being connected to one voltage level,
said input terminal being connected to the other voltage level,
a unijunction transistor having two bases and an emitter,
a resistor, said resistor being connected between one base and said one voltage level,
means for electrically connecting said one base to said gate and means for connecting the other base to said other voltage level,
means for providing rectified alternating voltage to the gate of the unijunction transistor, said providing means including means for varying the peak to peak voltage level of said rectified alternating current from a predetermined minimum value and to a predetermined maximum value,
a normally open relay connected in series between said other voltage level and said motor input terminal, and
means for periodically closing said relay for a predetermined angular rotation of said motor shaft.

6 more elements

Dependencies are inferred from the claim text.