Overvoltage protection circuit for dual outputs of opposite polarity

Claim 2

An overvoltage protective circuit for two output circuits having output voltages of opposite polarity, comprising: a first output clamping means comprising a thyristor means having an anode connected to the positive output lead, a cathode connected to ground and a control terminal connected to said positive output lead through a reference diode, so that when the voltage in said positive output lead exceeds a predetermined value said reference diode conducts current to trigger said thyristor means into conduction and said positive output lead is clamped to approximately ground potential; a second output clamping means comprising a thyristor means having an anode connected to ground, a cathode connected to the negative output lead, and a control terminal connected to ground through a reference diode, so that when the voltage in said negative output lead exceeds a pRedetermined value said reference diode conducts current to trigger said thyristor means into conduction and said negative output lead is clamped to approximately ground potential; and, means interconnecting said first and second clamping means for triggering the thyristor means of one of said clamping means in response to triggering of the thyristor means of the other of said clamping means.

Claim 3

An overvoltage protective circuit as defined in claim 1 wherein said interconnecting means comprises a first transistor associated with said first clamping means and a second transistor associated with said second clamping means, each of said transistors being normally nonconductive and having a base connected between resistance means located in a lead extending between said positive and negative output leads, said resistance means defining a voltage divider, the collector-emitter path of said first and second transistors being respectively connected to the control terminal of the thyristor means associated with said first and second clamping means, so that clamping of the voltage level of either of said positive and negative output leads to approximately ground potential changes the voltage level in said voltage dividers and biases the transistor associated with the unclamped clamping means into conduction to trigger the other of said thyristor means and thereby clamp both outputs to approximately ground potential.

Claim 4

An overvoltage protective circuit as defined in claim 2 wherein said first transistor is an npn-transistor having a collector connected to said positive output lead and an emitter connected to said control terminal of said first thyristor means.

Claim 5

An overvoltage protective circuit as defined in claim 2 wherein said second transistor is a pnp-transistor having an emitter connected to said ground lead and a collector connected to said control terminal of said second thyristor means.

Claim 6

An overvoltage protective circuit as defined in claim 3 including a protective diode having an anode connected to the emitter of said first transistor and a cathode connected to the base thereof.

Claim 7

An overvoltage protective circuit as defined in claim 4 including a protective diode having an anode connected to the base of said second transistor and a cathode connected to the emitter thereof.

Claim 8

An overvoltage protective circuit as defined in claim 2 including a capacitor connected between said negative output lead and the base of said first transistor.

Claim 9

A cross coupled overvoltage protection circuit for a dual voltage power supply or the like having two outputs, the output voltages in the output leads being of opposite polarity relative to ground potential, comprising: a first crowbar circuit connected in the positive voltage output and comprising first thyristor means having an anode connected to the positive voltage output lead, a cathode connected to the ground lead and a control terminal connected to the positive voltage output lead, a reference diode connected in said control lead so that if the voltage on said positive output lead exceeds a predetermined value will cause said reference diode to conduct and trigger said thyristor means and clamp said positive output lead to approximately ground potential; a second crowbar circuit connected in said negative output lead and comprising a second thyristor means having an anode connected to said ground lead, a cathode connected to said negative output lead and a control terminal connected to said ground lead, a reference diode connected in said control lead so that if the voltage on said negative output lead exceeds a predetermined value will cause said reference diode to conduct and trigger said thyristor means into conduction and clamp the value of the voltage in said negative output lead to approximately ground potential; and, means interconnecting said crowbar circuits to trigger the other thyristor means in the event one of said thyristor means is triggered, to thereby clamp both outputs to approximately ground potential in the event an overvoltage condition occurs in either of said output leads.

Claim 10

A cross coupled overvoltage protection circuit for a dual voltage power supply or the like having two outputs, the output voltages in the output leads being of opposite polarity relative to ground potential, comprising: a first crowbar circuit connected in the positive voltage output and comprising first thyristor means having an anode connected to the positive voltage output lead, a cathode connected to the ground lead and a control terminal connected to the positive voltage output lead, a reference diode connected in said control lead so that if the voltage on said positive output lead exceeds a predetermined value will cause said reference diode to conduct and trigger said thyristor means and clamp said positive output lead to approximately ground potential; a second crowbar circuit connected in said negative output lead and comprising a second thyristor means having an anode connected to said ground lead, a cathode connected to said negative output lead and a control terminal connected to said ground lead, a reference diode connected in said control lead so that if the voltage on said negative output lead exceeds a predetermined value will cause said reference diode to conduct and trigger said thyristor means into conduction and clamp the value of the voltage in said negative output lead to approximately ground potential; and, means interconnecting said crowbar circuits to trigger the other thyristor means in the event one of said thyristor means is triggered, to thereby clamp both outputs to approximately ground potential in the event an overvoltage condition occurs in either of said output leads.

Claim 11

A cross coupled overvoltage protection circuit as defined in claim 8 wherein said interconnecting means comprises first and second transistors respectively associated with said first and second crowbar circuits, each of said transistors being nonconductive when said thyristors are nonconductive, each of said transistors having its base connected intermediate resistance means connected in respective leads extending between said positive and negative output leads, said resistance means defining a voltage divider that is balanced so that the bases of each of said transistors are approximately at zero potential when said thyristor means are nonconductive, the collector-emitter path of said first and second transistors being respectively connected to the control terminal of said first and second thyristor means, the triggering of one of said thyristor means in response to an overvoltage condition on the output lead in which the crowbar circuit is located causing a voltage change in the voltage dividers which biases the transistor associated with the other crowbar circuit into conduction to trigger the other thyristor means and thereby clamp both outputs to approximately ground potential.

Claim 12

A cross coupled overvoltage protection circuit as defined in claim 8 wherein said first transistor is an npn-transistor having a collector connected to said positive output lead and an emitter connected to said control terminal of said first thyristor means.

Claim 13

A cross coupled overvoltage protection circuit as defined in claim 8 wherein said second transistor is a pnp-transistor having an emitter connected to said ground lead and a collector connected to said control terminal of said second thyristor means.