Motor control circuit

Claim 2

A motor speed control circuit comprising: an SCR device coupled in a series loop circuit with a motor armature for controlling the energy flow thereto; means for applying a rectified but pulsating voltage across said series loop circuit; means for producing a first voltage feedback signal substantially proportional to the voltage applied to the motor armature; means for producing a second voltage feedback signal substantially proportional to the current drawn by the motor armature; signal responsive means responsive to both of said feedback signals for producing a composite control signal as a function of a plurality of cycles of both of said feedback signals; and control means coupled in parallel with said SCR device and energized by the voltage existing between anode and cathode thereof, said control means having an input coupled to said signal responsive means for receiving said composite control signal and having an output coupled to the gate terminal of said SCR device for selectively initiating current flow through said SCR device, whereby each time that said SCR device commences to conduct the voltage between its anode and cathode drops to about a fraction of a volt and the energizing voltage for said control means drops accordingly.

Claim 3

A motor speed control circuit as claimed in claim 1 wherein said second voltage feedback signal producing means includes a resistor coupled in series with the motor armature, and which further includes a capacitor coupled in parallel with the series combination of said armature and resistor.

Claim 4

A motor speed control circuit as claimed in claim 2 which further includes a diode coupled in parallel with said capacitor and poled oppositely to said SCR device.

Claim 5

A motor speed control circuit as claimed in claim 2 wherein said signal responsive means includes an electron discharge device having first and second control electrodes coupled to said first and second voltage feedback signal producing means, respectively, and having an output electrode, and further including a storage capacitor coupled to said output electrode.

Claim 6

A motor speed control circuit as claimed in claim 2 wherein said first voltage feedback signal producing means includes an additional pair of resistors coupled in series with each other and in parallel across said series combination of armature and resistor.

Claim 7

A motor speed control circuit as claimed in claim 4 wherein said signal responsive means includes an electron discharge device having first and second control electrodes coupled to said first and second voltage feedback signal producing means, respectively, and having an output electrode, and further including a storage capacitor coupled to said output electrode.

Claim 8

A motor speed control circuit as claimed in claim 1 wherein said signal responsive means includes an electron discharge device having first and second control electrode coupled to said first and second voltage feedback signal producing means, respectively, anD having an output electrode, and further including a storage capacitor coupled to said output electrode.

Claim 9

A motor speed control circuit as claimed in claim 7 wherein said control means includes a unijunction transistor, a firing capacitor, a transistor regulating current flow to said firing capacitor, and a Zener diode regulating the voltage supplied to the series combination of said firing capacitor and transistor.

Claim 10

A motor speed control circuit as claimed in claim 1 wherein said control means includes a unijunction transistor, a firing capacitor, a transistor regulating current flow to said firing capacitor, and a Zener diode regulating the voltage supplied to the series combination of said firing capacitor and transistor.

Claim 11

A motor speed control circuit comprising: a rectifier, an SCR device, and a storage capacitor coupled together in a series loop circuit; an alternating current source coupled to said rectifier; means for coupling the motor armature in parallel with said storage capacitor; means coupled in parallel with said storage capacitor for developing feedback signals from the motor armature; and a firing control circuit for controlling the firing angle of said SCR device during each half-cycle of voltage applied through said rectifier, said firing control circuit being connected between anode and cathode of said SCR device for receiving operating energy when said SCR device is nonconductive, having an input not directly connected to said SCR device but coupled to said feedback developing means for receiving said feedback signals therefrom, and having an output connected to the gate lead of said SCR device for selectively initiating conduction of said device.

Claim 12

A motor speed control circuit comprising: a rectifier, an SCR device, and a storage capacitor coupled together in a series loop circuit; an alternating current source coupled to said rectifier; means for coupling the motor armature in parallel with said storage capacitor; means coupled in parallel with said storage capacitor for developing feedback signals from the motor armature; and a firing control circuit for controlling the firing angle of said SCR device during each half-cycle of voltage applied through said rectifier, said firing control circuit being connected between anode and cathode of said SCR device for receiving operating energy when said SCR device is nonconductive, having an input not directly connected to said SCR device but coupled to said feedback developing means for receiving said feedback signals therefrom, and having an output connected to the gate lead of said SCR device for selectively initiating conduction of said device.

Claim 13

A motor speed control circuit as claimed in claim 10 wherein said feedback developing means includes a resistor coupled in series with the motor armature, the series combination of said resistor and motor armature being coupled in parallel with said storage capacitor; and means for deriving across said resistor a voltage signal proportional to armature current.

Claim 14

A motor speed control circuit as claimed in claim 11 which includes a voltage divider coupled in parallel with said storage capacitor, and means for deriving from said voltage divider a voltage signal proportional to armature voltage.

Claim 15

A motor speed control circuit as claimed in claim 12 wherein said firing control circuit includes a transistor having two input electrodes to which said two voltage signals are respectively coupled, and an output electrode to which is coupled a load circuit including a capacitor and resistor connected in parallel.

Claim 16

A motor speed control circuit as claimed in claim 10 which includes a voltage divider coupled in parallel with said storage capacitor, and means for deriving from said voltage divider a voltage signal proportional to armature voltage.

Claim 17

A motor speed control circuit having provision for limiting the armature current to a predetermined safe value, comprising: a rectifier, an SCR device, and a motor armature coupled together in a series loop circuit; an alternating current source coupled to said rectifier; a firing circuit for controlling the firing of said SCR device during each half cycle of the alternating voltage that passes through said rectifier; means associated with said armature for developing regenerative feedback control signals; a control circuit responsive to said control signals when the armature load increases to actuate said firing circuit so as to increase the armature voltage, said control circuit including a first transistor having a bias current path, a second transistor having its emitter-collector current path connected as a series portion of said bias current path, means normally biasing said second transistor to a conductive state so that said first transistor is normally conductive and circuit means for normally delivering actuating current through the emitter-colleCtor path of said first transistor to said firing circuit; and circuit means responsive to the armature current, as said predetermined safe value is approached, for interrupting said normal biasing means to thereby open the bias current path of said first transistor.

Claim 18

A motor speed control circuit having provision for limiting the armature current to a predetermined safe value, comprising: a rectifier, an SCR device, and a motor armature coupled together in a series loop circuit; an alternating current source coupled to said rectifier; a firing circuit for controlling the firing of said SCR device during each half cycle of the alternating voltage that passes through said rectifier; means associated with said armature for developing regenerative feedback control signals; a control circuit responsive to said control signals when the armature load increases to actuate said firing circuit so as to increase the armature voltage, said control circuit including a first transistor having a bias current path, a second transistor having its emitter-collector current path connected as a series portion of said bias current path, means normally biasing said second transistor to a conductive state so that said first transistor is normally conductive and circuit means for normally delivering actuating current through the emitter-colleCtor path of said first transistor to said firing circuit; and circuit means responsive to the armature current, as said predetermined safe value is approached, for interrupting said normal biasing means to thereby open the bias current path of said first transistor.

Claim 19

A motor speed control circuit as claimed in claim -5 which includes a voltage divider having a midpoint connected to the base of said second transistor, a resistor connected in series with the armature in said series loop circuit so as to produce a control voltage proportional to armature current, said voltage divider having one of its ends connected to one end of said resistor, the base-emitter path of said second transistor being connected to the other end of said resistor.