Load control system employing silicon controlled rectifiers with overvoltage protection and compensation for line voltage fluctuations

Claim 2

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, a pair of silicon controlled rectifiers disposed in circuit between said input and output terminals with one connected in a polarity direction reversed with respect to the other, wherein said rectifiers are adapted to conduct current from said source to said load on opposite polarity half cycles, and a drive circuit coupled across the principal current carrying terminals of a said silicon controlled rectifier, said drive circuit including first means for controllably triggering operation of said last mentioned rectifier by driving the gate of said rectifier for turning on said rectifier during successive alternating current half cycles of a given polarity and in predetermined phase relation therewith, the drive energy applied to said gate for turning on said rectifier being principally derived from across said silicon controlled rectifier, and second means responsive to the voltage across the principal current carrying terminals of said silicon controlled rectifier for also triggering operation of said silicon controlled rectifier if the voltage thereacross reaches a predetermined excessive value in order to protect the remaining silicon controlled rectifier from an overvoltage condition.

Claim 3

The system according to claim 1 wherein said first means includes a capacitor charged from across said silicon controlled rectifier and controL means for discharging said capacitor into the gate of said rectifier, said control means having a first triggerable terminal operable in predetermined controllable phase relation with successive alternating current half cycles of said given polarity to bring about conduction of said control means to discharge said capacitor.

Claim 4

The system according to claim 2 wherein said control means comprises a unijunction transistor disposed between said capacitor and the gate of said rectifier.

Claim 5

The system according to claim 3 further including a transformer for receiving triggering pulses in predetermined phase relation with successive alternating current half cycles, said first triggerable terminal comprising the gate of said unijunction transistor coupled in driven relation to a secondary of said transformer.

Claim 6

The system according to claim 2 where said second means comprises means for applying at least a portion of the voltage across said rectifier to a triggerably terminal of said control means.

Claim 7

The system according to claim 5 wherein said control means comprises a unijunction transistor, the last mentioned triggerable terminal comprising an anode terminal thereof, and said first triggerable terminal comprising the gate terminal thereof.

Claim 8

The system according to claim 1 wherein said first means comprises a capacitor and a charging circuit including a diode for charging said capacitor from across said silicon controlled rectifier, said first means further including a unijunction transistor coupling said capacitor to the gate of said silicon controlled rectifier for discharging said capacitor into said gate of said silicon controlled rectifier as said unijunction transistor is operated, said first means further including a trigger transformer having a secondary disposed between the charged end of said capacitor and the gate of said unijunction transistor, and a diode disposed between the charged end of said capacitor and the anode of said unijunction transistor, the last mentioned diode being poled in a common polarity direction with the first mentioned diode and said unijunction transistor, said second means comprising a voltage divider coupled across said rectifier via said first mentioned diode, wherein a tap on said voltage divider is coupled to the anode of said unijunction transistor.

Claim 9

The system according to claim 7 further including a Zener diode coupled across said capacitor and a resistance between said Zener diode and the first mentioned diode.

Claim 10

The system according to claim 8 further including a dropping resistor between said unijunction transistor and the gate of said rectifier.

Claim 11

The system according to claim 2 including a transformer the secondary of which is coupled to the first triggerable terminal, and means for triggering the primary of said transformer, said last mentioned means comprising: a switching circuit coupled to said input terminal and adapted to provide a current flow path during each half cycle of current from said source, a second capacitor adapted to be charged from said current flow path and semiconductor means triggerable from the charge of said second capacitor for energizing the primary of said transformer, controllable means for adjusting the charge delivered to said second capacitor via said current flow path, and resistive means for providing an additional current flow path to said second capacitor.

Claim 12

The system according to claim 10 further including a power supply coupled to said input terminal and providing the current in the first mentioned current flow path as well as providing control current at said semiconductor means proportional to the voltage at the input terminal for causing said semiconductor means and said control means to be operable in said predetermined phase relation at an earlier time with a decrease in voltage at said input terminal, and later with an increase in voltage at said input terminal, for lessening variation in the output delivEred at said output terminal.

Claim 13

The system according to claim 11 wherein said semiconductor means comprises a unijunction transistor deriving its gate voltage from said power supply.

Claim 14

The system according to claim 11 wherein said controllable means comprises a semiconductor device included in the first mentioned current flow path, and means for applying a control input to said semiconductor device.

Claim 15

The system according to claim 11 wherein said switching circuit provides the said control current by way of the first mentioned current flow path.

Claim 16

The system according to claim 11 wherein said power supply also provides current in said additional current flow path, with the said control current predominating in proportional effect whereby to operate said semiconductor means for lessening the effect of input voltage changes.

Claim 17

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, a pair of silicon controlled rectifiers disposed in circuit between said input and output terminals with one connected in a polarity direction reversed with respect to the other, wherein said rectifiers are adapted to conduct current from said source to said load on opposite polarity half cycles, and a drive circuit coupled across the principal current carrying terminals of a said silicon controlled rectifier, said drive circuit including means for controllably triggering operation of said last mentioned rectifier by driving the gate of said rectifier for turning on said rectifier during successive alternating current half cycles of a given polarity and in predetermined phase relation therewith, said means including a capacitor charged from across said silicon controlled rectifier, and semiconductor control means for discharging said capacitor into the gate of said rectifier, said semiconductor control means having a first triggerable terminal operable in predetermined controllable phase relation with successive alternating current half cycles of said given polarity to bring about conduction of said control means to discharge said capacitor, and a transformer having a winding coupled to said first triggerable terminal for receiving a control signal in said predetermined phase relation.

Claim 18

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, a pair of silicon controlled rectifiers disposed in circuit between said input and output terminals with one connected in a polarity direction reversed with respect to the other, wherein said rectifiers are adapted to conduct current from said source to said load on opposite polarity half cycles, and a drive circuit coupled across the principal current carrying terminals of a said silicon controlled rectifier, said drive circuit including means for controllably triggering operation of said last mentioned rectifier by driving the gate of said rectifier for turning on said rectifier during successive alternating current half cycles of a given polarity and in predetermined phase relation therewith, said means including a capacitor charged from across said silicon controlled rectifier, and semiconductor control means for discharging said capacitor into the gate of said rectifier, said semiconductor control means having a first triggerable terminal operable in predetermined controllable phase relation with successive alternating current half cycles of said given polarity to bring about conduction of said control means to discharge said capacitor, and a transformer having a winding coupled to said first triggerable terminal for receiving a control signal in said predetermined phase relation.

Claim 19

The system according to claim 16 wherein the remaining silicon controlled rectifier is provided with a substantially similar but separate drive circuit.

Claim 20

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, a pair of silicon controlled rectifiers disposed in circuit between said input and output terminals with one connected in a polarity direction reversed with respect to the other, wherein said rectifiers are adapted to conduct current from said source to said load on opposite polarity half cycles, and means connected directly across the principal current carrying terminals of a said silicon controlled rectifier for triggering operation thereof when the voltage thereacross exceeds a predetermined excessive value, in order to protect the remaining silicon controlled rectifier from an inverse overvoltage condition.

Claim 21

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, a pair of silicon controlled rectifiers disposed in circuit between said input and output terminals with one connected in a polarity direction reversed with respect to the other, wherein said rectifiers are adapted to conduct current from said source to said load on opposite polarity half cycles, and means connected directly across the principal current carrying terminals of a said silicon controlled rectifier for triggering operation thereof when the voltage thereacross exceeds a predetermined excessive value, in order to protect the remaining silicon controlled rectifier from an inverse overvoltage condition.

Claim 22

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, silicon controlled rectifier means disposed in circuit between said input and output terminals, d.c. power supply means energized from said input terminal, control means for providing a predetermined output with each half cycle of the alternating current input applied to said input terminal, for application to said silicon controlled rectifier means At predetermined times relative to each half cycle of alternating current input, said control means comprising a capacitor charged during each half cycle of alternating current input and unijunction transistor means having its anode-cathode path coupled to said capacitor for being triggered by the charge on said capacitor and for thereupon triggering said silicon controlled rectifier means the gate of said unijunction transistor means being coupled to the output of said d.c. power supply means for providing a further control in operation of said unijunction transistor for detecting changes in the output of said power supply for advancing the triggering of said silicon controlled rectifier means as the power supply output decreases and for retarding the triggering of said silicon controlled rectifier means as the power supply output increases.

Claim 23

In a load control system, an input terminal adapted to be connected to a source of alternating current, an output terminal adapted to be connected to a load to which an adjustable amount of power is to be delivered, silicon controlled rectifier means disposed in circuit between said input and output terminals, d.c. power supply means energized from said input terminal, control means for providing a predetermined output with each half cycle of the alternating current input applied to said input terminal, for application to said silicon controlled rectifier means At predetermined times relative to each half cycle of alternating current input, said control means comprising a capacitor charged during each half cycle of alternating current input and unijunction transistor means having its anode-cathode path coupled to said capacitor for being triggered by the charge on said capacitor and for thereupon triggering said silicon controlled rectifier means the gate of said unijunction transistor means being coupled to the output of said d.c. power supply means for providing a further control in operation of said unijunction transistor for detecting changes in the output of said power supply for advancing the triggering of said silicon controlled rectifier means as the power supply output decreases and for retarding the triggering of said silicon controlled rectifier means as the power supply output increases.

Claim 24

The system according to claim 19 wherein said control means further includes an adjustable element for controlling charge current to said capacitor.