Firing control circuit for grid-controlled switching devices

Claim 2

A circuit comprising: a. a switching circuit connected to receive an AC input voltage, said switching circuit having at least one grid-controlled means for rectifying an AC signal connected in circuit and having a pair of output terminals for presenting a DC output signal, the duty cycle of the DC output signal being controlled at a selectively variable predetermined firing angle of said grid-controlled rectifying means; b. a logic circuit means for controlling the firing angle of said rectifying means during each cycle of said AC voltage, said logic circuit means beinG phase-referenced to said AC signal, said logic circuit means adapted to generate gating pulses having a predetermined pulse width, said logic circuit generating a first gating pulse at a selectively variable firing angle in each cycle of the AC voltage, said first gating pulse coupled to gate said grid-controlled rectifying means into conduction; and c. an inhibitor circuit means having an input coupled to said grid-controlled rectifying means for monitoring the state of conduction in said grid-controlled rectifying means and having an output coupled to said logic circuit means for enabling said logic circuit whenever said rectifying means is not conducting and for disabling said logic circuit means beginning a predetermined time from each firing of said rectifying means by each gating pulse in each cycle, said logic circuit means generating a subsequent gating pulse after said first gating pulse in each said cycle whenever said logic circuit means is enabled by said inhibitor circuit means, each subsequent gating pulse gating said grid-controlled rectifying means into conduction.

Claim 3

The device as claimed in claim 1 wherein said switching circuit comprises a rectifier circuit, and said logic circuit means comprises an AC reference circuit means, a means for supplying a controlled voltage and a comparator circuit, said AC reference circuit means coupled to receive the AC voltage for producing an AC reference voltage shifted in phase from said AC voltage by a predetermined angle, the control voltage being selectively variable and corresponding to a predetermined angle with respect to a cycle of the AC voltage, said comparator circuit means having an input coupled to said means for supplying a control voltage to receive said control voltage, said comparator circuit means summing said AC reference voltage and said control voltage to generate said first gating pulse at a predetermined angle with respect to a cycle of the AC voltage, said rectifier circuit presenting a DC output voltage, the magnitude of the DC output voltage being proportional to the firing angle of said grid-controlled rectifying means.

Claim 4

The devices claimed in claim 2 wherein said rectifier circuit comprises a half-controlled, single-phase bridge rectifier circuit.

Claim 5

The devices claimed in claim 2 wherein said rectifier circuit comprises a half-controlled, three-phase bridge rectifier circuit.

Claim 6

A speed-controlled DC motor comprising: a. a DC motor; b. a rectifier circuit connected to receive an AC input voltage, said rectifier circuit having at least one grid-controlled means for rectifying an AC voltage connected in circuit and having a pair of output terminals for presenting a DC output voltage, the magnitude of the DC output voltage being proportional to the firing angle of said grid-controlled rectifying means, said DC output voltage coupled to the armature of said DC motor, the speed of said DC motor being proportional to the magnitude of said DC output voltage; c. a logic circuit means for controlling the firing angle of said rectifying means during each cycle of said AC input voltage, said logic circuit means being phase-referenced to said AC input signal, said logic circuit means adapted to generate gating pulses having a predetermined pulse width, said logic circuit means generating a first gating pulse at a selectively variable firing angle in each cycle of the AC input voltage, said first gating pulse coupled to gate said grid-controlled rectifying means into conduction; and d. an inhibitor circuit means having an input coupled to said grid-controlled rectifying means for monitoring the state of conduction in said grid-controlled rectifying means and having an output coupled to said logic circuit means for enabling said logic circuit means whenever said rectifying means is not conducting and for disabling said logic circuit means, said inhibitor circuit means disabling said logic circuit means beginning a predetermiNed time from each firing of said rectifying means by each gating pulse in each cycle, said logic circuit generating a subsequent gating pulse after said first gating pulse in each said cycle whenever said logic circuit is enabled by said inhibitor circuit, each subsequent gating pulse gating said grid-controlled rectifying means into conduction.

Claim 7

A speed-controlled DC motor comprising: a. a DC motor; b. a rectifier circuit connected to receive an AC input voltage, said rectifier circuit having at least one grid-controlled means for rectifying an AC voltage connected in circuit and having a pair of output terminals for presenting a DC output voltage, the magnitude of the DC output voltage being proportional to the firing angle of said grid-controlled rectifying means, said DC output voltage coupled to the armature of said DC motor, the speed of said DC motor being proportional to the magnitude of said DC output voltage; c. a logic circuit means for controlling the firing angle of said rectifying means during each cycle of said AC input voltage, said logic circuit means being phase-referenced to said AC input signal, said logic circuit means adapted to generate gating pulses having a predetermined pulse width, said logic circuit means generating a first gating pulse at a selectively variable firing angle in each cycle of the AC input voltage, said first gating pulse coupled to gate said grid-controlled rectifying means into conduction; and d. an inhibitor circuit means having an input coupled to said grid-controlled rectifying means for monitoring the state of conduction in said grid-controlled rectifying means and having an output coupled to said logic circuit means for enabling said logic circuit means whenever said rectifying means is not conducting and for disabling said logic circuit means, said inhibitor circuit means disabling said logic circuit means beginning a predetermiNed time from each firing of said rectifying means by each gating pulse in each cycle, said logic circuit generating a subsequent gating pulse after said first gating pulse in each said cycle whenever said logic circuit is enabled by said inhibitor circuit, each subsequent gating pulse gating said grid-controlled rectifying means into conduction.