Overvoltage protection circuit

Claim 2

An overvoltage clamping circuit for protecting of a direct current power source means against abnormal voltage conditions comprising a temperature stable solid state three terminal voltage comparator having input terminals connected respectively to the power source, a reference voltage and ground and responsive to abnormal deviations of said power source voltage from a selected reference voltage and establishing a selected control signal at a control terminal only upon sensing an abnormal deviation, a solid state power switch connected across said direct current power source to define an essentially short circuit when conducting, and triggering circuit means connecting the control terminal of said voltage comparator to said controlled solid state power switch and responsive to a selected overvoltage condition to trigger said switch and establish said essentially short circuit condition.

Claim 3

The overvoltage clamping circuit of claim 1 including a current limit disconnect means connected to the direct current power source means and responsive to said essentially short circuit condition to open the power source means.

Claim 4

The overvoltage clamping circuit of claim 1 wherein said direct currEnt power source means includes an internal voltage regulator and having a voltage dividing network connected to the reference voltage of the regulator, said solid state power switch being a controlled rectifier means.

Claim 5

The clamping circuit of claim 1 wherein said comparator is a programmable unijunction transistor having a main output circuit means connected directly across the gate of a power switch having an anode means connected to the direct current source means and a gate means connected to the reference voltage, said power switch having a control connected to the programmable unijunction transistor whereby an increase in the anode voltage over the gate reference voltage results in triggering of the unijunction transistor with a consequent turn-on of the power switch to establish an essentially short circuit across the output of the power source means.

Claim 6

The overvoltage clamping circuit of claim 1 for protection of a low voltage power source having an internal voltage regulator establishing a normal operating voltage, said solid state power switch being triggered by unidirectional conducting means connected directly across the low voltage power source, said switch having a triggering input gate, a voltage dividing network connected to said voltage regulator and having an adjustable resistance means to establish a reference voltage with respect to said operating voltage, said solid state three terminal voltage comparator including a programmable unijunction transistor having a main input circuit means connected across the power source through a gating resistor and having a gate means connected to the voltage dividing network, the input gate of said power switch being connected to the junction of said gating resistor and output of the programmable unijunction transistor.

Claim 7

The clamping circuit of claim 5 having a capacitor connected across said adjustable resistance, and a protecting capacitor connected across the unijunction transistor and said gating resistor.

Claim 8

The overvoltage clamping circuit of claim 1 for protection of a direct current regulated low voltage power source establishing a normal operating voltage wherein said solid state power switch is a controlled rectifier connected directly across the voltage power source, said switch having a triggering input gate, said voltage power source having an internal reference voltage means, a voltage dividing network connected to said reference voltage means to establish a reference voltage with respect to said operating voltage, said comparator including a programmable unijunction transistor having a main input circuit means connected across the voltage power source and having a gate means connected to the voltage dividing network, said power rectifier having its gate connected to the output terminal of the programmable unijunction transistor, the gate voltage on the unijunction transistor being above the voltage on the anode of the unijunction transistor with the operating voltage below a selected level, whereby an increase in the anode voltage over the gate reference voltage results in triggering of the unijunction transistor with a consequent firing of the power rectifier to establish said essentially short circuit across the output of the voltage power source.

Claim 9

The overvoltage clamping circuit of claim 1 wherein said direct current power source means includes a pair of opposite polarity voltage sources having a common reference and comprising a voltage monitoring network connected directly across both power sources and having a set point adjustment means for selecting a portion of the voltage, said comparator including a unilateral three terminal switch having input and output terminals and a compensating terminal, said input terminal being connected to said network and said output terminal being connected to said triggering circuit means, said unilateral switch being responsive to a selected voltage difference at said terminals to conduct and establish a voltage signal at said control tErminal said power switch including a pair of conducting means connected across each of said voltage sources and having a gate means connected to said triggering circuit means for simultaneous actuation.

Claim 10

The clamping circuit of claim 8 having a controlled rectifier ampliifer connected between said voltage sources and including a controlled rectifier in series with a diode and a resistor, said controlled rectifier amplifier having a gate connected to said control terminal of said unilateral switch to turn on said controlled rectifier amplifier in response to triggering of the unilateral switch, a first voltage dividing network connected between the output of the trigger controlled rectifier and the one voltage source, a second trigger voltage dividing network connected between the side of the diode and the common reference ground, said pair of conducting means including first and second power controlled rectifiers connected one each across said pair of voltage sources and having gates connected respectively one each to the voltage dividing networks to provide essentially simultaneous firing of the power controlled rectifiers in response to conduction through the controlled rectifier amplifier to thereby establish corresponding essentially short circuiting clamps across each of the sources.

Claim 11

The overvoltage clamping circuit of claim 8 having an amplifier connected to said power sources and having an input means connected to said control terminal of said unilateral switch to turn on said amplifier in response to triggering of the unilateral switch, and connecting means connecting the output of the amplifier to said gate means of said pair of conducting means.

Claim 12

The overvoltage clamping circuit of claim 10 wherein said connecting means includes a first voltage dividing network connected between the output of the amplifier and the one voltage source, a second voltage dividing network connected between the amplifier and the common reference ground, said conducting means having first and second gates connected respectively one each to the voltage dividing networks to provide essentially simultaneous conduction in response to conduction through the amplifier to thereby establish corresponding essentially short circuiting clamps across each of the sources.

Claim 13

A dual overvoltage crowbar circuit for protecting of a pair of opposite polarity voltage sources having a common reference and each of which includes an individual current limiting means, comprising a voltage monitoring or sensing network connected directly across both power supplies and having an intermediate set point adjustment tap means for selecting a portion of the voltage between the tap and the respective power sources, a unilateral three terminal switch having input and output terminals and a compensating terminal, said input terminal being connected to said tap and said compensating terminal being connected to one of the power sources, said unilateral switch being responsive to a selected voltage different at said input and output terminals to conduct and establish a voltage signal at said output terminal, a controlled rectifier amplifier connected between said power supplies and including a controlled rectifier in series with a diode and a resistor, said controlled rectifier amplifier having a gate connected to said output terminal to turn on said controlled rectifier amplifier in response to triggering of the unilateral switch, a first voltage dividing network connected between the output of the trigger controlled rectifier and the one power supply, a second trigger voltage dividing network connected between the output side of the diode and the common reference ground, first and second power controlled rectifiers connected one each across said pair of voltage sources and having gates connected respectively one each to the voltage dividing networks to provide essentially simultaneous firing of the power controlled rectifiers in response to conduction through the controlled rectifier amplifier to thereby Establish corresponding essentially short circuiting clamps across each of the sources.

Claim 14

A dual overvoltage crowbar circuit for protecting of a pair of opposite polarity voltage sources having a common reference and each of which includes an individual current limiting means, comprising a voltage monitoring or sensing network connected directly across both power supplies and having an intermediate set point adjustment tap means for selecting a portion of the voltage between the tap and the respective power sources, a unilateral three terminal switch having input and output terminals and a compensating terminal, said input terminal being connected to said tap and said compensating terminal being connected to one of the power sources, said unilateral switch being responsive to a selected voltage different at said input and output terminals to conduct and establish a voltage signal at said output terminal, a controlled rectifier amplifier connected between said power supplies and including a controlled rectifier in series with a diode and a resistor, said controlled rectifier amplifier having a gate connected to said output terminal to turn on said controlled rectifier amplifier in response to triggering of the unilateral switch, a first voltage dividing network connected between the output of the trigger controlled rectifier and the one power supply, a second trigger voltage dividing network connected between the output side of the diode and the common reference ground, first and second power controlled rectifiers connected one each across said pair of voltage sources and having gates connected respectively one each to the voltage dividing networks to provide essentially simultaneous firing of the power controlled rectifiers in response to conduction through the controlled rectifier amplifier to thereby Establish corresponding essentially short circuiting clamps across each of the sources.