Transient voltage protection circuit for gate turn on devices

Claim 3

A protective circuit for a gate turn-on device controlling a flow of electricity between a power source and a load, said device having a power terminal, a firing terminal and a common terminal, said circuit comprising a junction, means providing a DC reference potential connected between said junction and the common terminal, a unijunction device connected to selectively conduct a firing current between said junction ad the firing terminal, said unijunction device having a control terminal, and means supplying to said control terminal a variable potential inversely proportional to an instantaneous voltage applied between the power and common terminals whereby said unijunction device is rendered conductive when the variable potential falls below said reference potential.

Claim 4

A protective circuit for a gate turn-on device controlling a flow of electricity between a power source and a load, said device having a power terminal, a firing terminal and a common terminal, said circuit comprising a junction, means providing a DC reference potential connected between said junction and the common terminal, a unijunction device connected to selectively conduct a firing current between said junction ad the firing terminal, said unijunction device having a control terminal, and means supplying to said control terminal a variable potential inversely proportional to an instantaneous voltage applied between the power and common terminals whereby said unijunction device is rendered conductive when the variable potential falls below said reference potential.

Claim 5

A protective circuit as in claim 2, said means supplying the DC reference potential comprising a capacitor having a first plate connected to the common terminal and a second plate connected to said junction, means connected between the junction and said power terminal to delay charging of said capacitor, a unidirectional conductor in series with the delay means between the junction and said power terminal, and means limiting said DC reference potential.

Claim 6

A protective circuit as in claim 2, in which the unijunction device is a two layer PN unijunction transistor having an emitter connected to said junction, a base-one connected to said firing terminal, and a base-two comprising said control terminal.

Claim 7

A protective circuit as in claim 2, in which the unijunction device is a four layer PN programmable unijunction transistor having an anode, a cathode and an anode gate, said anode connected to the junction, said cathode connected to the firing terminal, and said anode gate comprising the control terminal.

Claim 8

A protective circuit as in claim 2, said means supplying the variable potential comprising a voltage divider connected to be energized in proportion to the instantaneous voltage applied between said power and common terminals, said voltage divider having a tap providing an intermediate voltage, and an inverting amplifier providing said variable potential as an output in response to the intermediate voltage received from said tap as an input.

Claim 9

A protective circuit as in claim 6, said amplifier comprising a transistor having a base connected to said tap, a collector connected to the control terminal and a common emitter connected to said common terminal, and a load resistance connected between the power terminal and said collector.

Claim 10

A protective circuit as in claim 2 with the addition of means for electrically isolating said circuit from the power terminal.

Claim 11

A protective circuit as in claim 8, in which the isolating means is a transformer.

Claim 12

A protective circuit for a bidirectional gate turn-on device controlling flow of an AC current between first and second conductors, said device having first and second terminals connected to said respective first and second conductors and a firing terminal, said circuit comprising a voltage divider connected between said first and second conductors, a tap on said voltage divider, a first capacitor having a first positive plate connected to the second conductor and a first negative plate, a first rectifier connected to conduct current from said second to said first conductor, a first current-limiting resistor in series with said first rectifier between the first negative plate and the first conductor, a first voltage limiting resistor in parallel with said first capacitor, a second capacitor having a second negative plate connected to the second conductor and a second positive plate, a second rectifier connected to conduct current from said first conductor to said second positive plate, a second current limiting resistor in series with said second rectifier between the second positive plate and the first conductor, a second voltage limiting resistor in parallel with said second capacitor, a PNP transistor, an NPN transistor, each of said transistors having a base an emitter and a collector, said bases being connected to the tap, said emitters being connected to the second conductor, a pair of load resistors connected between respective ones of said collectors and the first conductor, a first unijunction device connected to conduct current from said firing terminal to the first negative plate and having a first control terminal connected to the collector of said PNP transistor, and a second unijunction device connected to conduct current from said second positive plate to the firing terminal and having a second control terminal connected to the collector of said NPN transistor.

Claim 13

A protective circuit for a bidirectional gate turn-on device controlling flow of an AC current between first and second conductors, said device having first and second terminals connected to said respective first and second conductors and a firing terminal, said circuit comprising a voltage divider connected between said first and second conductors, a tap on said voltage divider, a first capacitor having a first positive plate connected to the second conductor and a first negative plate, a first rectifier connected to conduct current from said second to said first conductor, a first current-limiting resistor in series with said first rectifier between the first negative plate and the first conductor, a first voltage limiting resistor in parallel with said first capacitor, a second capacitor having a second negative plate connected to the second conductor and a second positive plate, a second rectifier connected to conduct current from said first conductor to said second positive plate, a second current limiting resistor in series with said second rectifier between the second positive plate and the first conductor, a second voltage limiting resistor in parallel with said second capacitor, a PNP transistor, an NPN transistor, each of said transistors having a base an emitter and a collector, said bases being connected to the tap, said emitters being connected to the second conductor, a pair of load resistors connected between respective ones of said collectors and the first conductor, a first unijunction device connected to conduct current from said firing terminal to the first negative plate and having a first control terminal connected to the collector of said PNP transistor, and a second unijunction device connected to conduct current from said second positive plate to the firing terminal and having a second control terminal connected to the collector of said NPN transistor.