Current limit circuit for a dc motor

Claim 2

A control circuit, for a direct current motor having an armature winding and a field winding, of the type employing phase controlled rectifiers to vary the effective voltage applied from an alternating current source to said motor, said control circuit comprising: a. means to determine the armature winding voltage and to provide a first signal proportional thereto; b. means to generate a second signal of varying magnitude beginning at a prescribed time after the beginning of each half cycle of said alternating current source; c. a reference signal generating means for generating a reference signal proportional to a desired phase angle of rendering said rectifiers conductive; and, d. means for combining said first, second and third signals to provide an inhibit signal operative to prevent the rendering of the controlled rectifiers conductive until said first, second and third signals are of a prescribed relationship.

Claim 3

The invention in accordance with claim 1 wherein said means to generate the second signal is a ramp function generator.

Claim 4

The invention in accordance with claim 1 wherein there is further included a phase displacement circuit for initiating the operation of the means to generate the second signal.

Claim 5

A control circuit, for a direct current motor having an armature winding and a field winding, of the type employing phase controlled rectifiers to vary the effective voltage applied from an alternating current source to said motor, said control circuit comprising: a. means to determine the armature winding voltage and to provide a first signal proportional thereto; b. means to generate a second signal of varying magnitude beginning at a prescribed time after the beginning of each half cycle of said alternating current source; c. combining means to combine said first and second signals and to provide an output signal indicative thereof; d. a reference signal generating means for generating a reference signal proportional to a desired phase angle of rendering said rectifiers conductive; and, e. means to compare said output signal and said reference signal to provide an inhibit signal operative to prevent the rendering of the controlled rectifiers conductive until said reference signal and said output signal are of a prescribed relationship.

Claim 6

A control circuit, for a direct current motor having an armature winding and a field winding, of the type employing phase controlled rectifiers to vary the effective voltage applied from an alternating current source to said motor, said control circuit comprising: a. means to determine the armature winding voltage and to provide a first signal proportional thereto; b. means to generate a second signal of varying magnitude beginning at a prescribed time after the beginning of each half cycle of said alternating current source; c. combining means to combine said first and second signals and to provide an output signal indicative thereof; d. a reference signal generating means for generating a reference signal proportional to a desired phase angle of rendering said rectifiers conductive; and, e. means to compare said output signal and said reference signal to provide an inhibit signal operative to prevent the rendering of the controlled rectifiers conductive until said reference signal and said output signal are of a prescribed relationship.

Claim 7

The invention in accordance with claim 4 wherein said means to generate the second signal is a ramp function generator.

Claim 8

The invention in accordance with claim 4 wherein there is further included a phase displacement circuit for initiating the operation of the means to generate the second signal.

Claim 9

The invention in accordance with claim 4 wherein said output signal and said reference signals are both current signals and said means to compare those signals includes a pair of transistors having matched electrical characteristics and having a common voltage applied to a base of each of said transistors.

Claim 10

The invention in accordance with claim 4 wherein said prescribed relationship is determined by the reference signal being greater than the output signal.

Claim 11

A control circuit for a direct current motor having an armature winding and a field winding supplied from a source of alternating current power, said control circuit comprising: a. a full wave rectification bridge for supplying unidirectional power from said source to said armature winding, said bridge having a controllable rectifier in each leg thereof; b. a firing circuit for rendering said rectifiers conductive at a prescribed phase angle with respect to the power from said source; c. means to determine the voltage of the armature winding and to provide a first signal proportional thereto; d. means to generate a second signal of varying magnitude beginning at a prescribed point in each half cycle of said alternating current source; e. combining means to combine said first and second signals and to provide an output signal indicative thereof; f. a reference signal generating means for generating a reference signal proportional to a desired phase angle of firing of said rectifiers; and, g. means to compare said output signal and said reference signal to provide an inhibit signal operative to prevent the firing of the control rectifiers so long as the value of said reference signal exceeds that of said output signal.

Claim 12

A control circuit for a direct current motor having an armature winding and a field winding supplied from a source of alternating current power, said control circuit comprising: a. a full wave rectification bridge for supplying unidirectional power from said source to said armature winding, said bridge having a controllable rectifier in each leg thereof; b. a firing circuit for rendering said rectifiers conductive at a prescribed phase angle with respect to the power from said source; c. means to determine the voltage of the armature winding and to provide a first signal proportional thereto; d. means to generate a second signal of varying magnitude beginning at a prescribed point in each half cycle of said alternating current source; e. combining means to combine said first and second signals and to provide an output signal indicative thereof; f. a reference signal generating means for generating a reference signal proportional to a desired phase angle of firing of said rectifiers; and, g. means to compare said output signal and said reference signal to provide an inhibit signal operative to prevent the firing of the control rectifiers so long as the value of said reference signal exceeds that of said output signal.

Claim 13

The invention in accordance with claim 9 wherein said controlled rectifiers are thyristors.

Claim 14

The invention in accordance with claim 9 wherein said means to generate the second signal is a ramp function generator.

Claim 15

The invention in accordance with claim 9 wherein there is further included a phase displacement circuit for initiating the operation of the means to generate the second signal.

Claim 16

The invention in accordance with claim 9 wherein said output signals and said reference signals are both current signals and said means to compare those signals includes a pair of transistors having matched electrical characteristics and having a common voltage applied to a base of each of said transistors.

Claim 17

A control circuit for a direct current motor having an armature winding adapted to be supplied with power from an alternating current power source through a thyristor rectifying bridge source, said control circuit comprising: a. a firing circuit for rendering the thyristors of said bridge conductive at a prescribed phase angle with respect to the voltage of the source; b. means to generate a first signal proportional to the current in said armature winding; c. means to generate a second signal of varying magnitude beginning a prescribed time in each half cycle of said alternating current source; d. combining means to combine said first and second signals and to provide an output signal indicative thereof; e. a reference signal generating means for generating a reference signal proportional to a desired phase angle for the rendering of the thyristors conductive; and, f. means to compare said output signal and said reference signal to provide an inhibit signal operative to inhibit the operation of said firing circuit until said reference signal and said output signal are of a prescribed relationship.

Claim 18

A control circuit for a direct current motor having an armature winding adapted to be supplied with power from an alternating current power source through a thyristor rectifying bridge source, said control circuit comprising: a. a firing circuit for rendering the thyristors of said bridge conductive at a prescribed phase angle with respect to the voltage of the source; b. means to generate a first signal proportional to the current in said armature winding; c. means to generate a second signal of varying magnitude beginning a prescribed time in each half cycle of said alternating current source; d. combining means to combine said first and second signals and to provide an output signal indicative thereof; e. a reference signal generating means for generating a reference signal proportional to a desired phase angle for the rendering of the thyristors conductive; and, f. means to compare said output signal and said reference signal to provide an inhibit signal operative to inhibit the operation of said firing circuit until said reference signal and said output signal are of a prescribed relationship.

Claim 19

The invention in accordance with claim 14 wherein prescribed relationship is determined by the reference signal being greater than the output signal.

Claim 20

The invention in accordance with claim 14 wherein said means to generate the second signal is a ramp function generator.

Claim 21

The invention in accordance with claim 14 wherein there is further included a phase displacement circuit for initiating the operation of the means to generate the second signal.

Claim 22

The invention in accordance with claim 14 wherein said output signal and said reference signals are both current signals and said means to compare those signals includes a pair of transistors having matched electrical characteristics and having a common voltage applied to a base of each of said transistors.

Claim 23

The invention in accordance with claim 14 wherein said reference signal generating means is adjustable.