High voltage breakover diode having comparable forward breakover and reverse breakdown voltages

Abstract

In a first embodiment, an ultra-fast breakover diode has a turn on time TON that is less than 0.3 microseconds, where the forward breakover voltage is greater than +400 volts and varies less than one percent per ten degrees Celsius change. In a second embodiment, a breakover diode has a reverse breakdown voltage that is greater, in absolute magnitude, than the forward breakover voltage, where the forward breakover voltage is greater than +400 volts. In a third embodiment, a string of series-connected breakover diode dice is provided, along with a resistor string, in a packaged circuit. The packaged circuit acts like a single breakover diode having a large forward breakover voltage and a comparably large reverse breakdown voltage, even though the packaged circuit includes no discrete high voltage reverse breakdown diode. The packaged circuit is usable to supply a triggering current to a thyristor in a voltage protection circuit.

Description

TECHNICAL FIELD[0001]The described embodiments relate to breakover diodes and to related structures and methods.BACKGROUND INFORMATION[0002]FIG. 1 (Prior Art) is a symbol of a thyristor 1. A conventional thyristor is a three terminal semiconductor device that has four layers of alternating N type material and P type material. FIG. 2 (Prior Art) shows an example in which the thyristor device 1 has an P-N-P-N structure. A cathode electrode 2 is coupled to the N type material on one side of the device and an anode electrode 3 is coupled to the P type material on the other side of the device. A gate electrode 4 is coupled to the P type layer closest to the cathode. The structure has three PN junctions, serially named J1, J2, and J3, from the anode electrode side of the device. Operation of the thyristor device is explained in terms of a pair of tightly coupled bipolar junction transistors, arranged in a self-latching way, as illustrated in FIG. 3 (Prior Art). One bipolar transistor 5 is...

AI Technical Summary

Benefits of technology

The packaged overvoltage protection circuit is designed to protect thyristors from excessive voltage spikes. When the voltage across the thyristor reaches a certain level, a series of breakover diodes in the circuit will fire, providing a triggering current to the thyristor. This current will reduce the voltage across the thyristor, preventing damage. The circuit can also include a snubber circuit to soften the impact of voltage spikes and a current limiting resistor to control the triggering current. The patent also describes a second circuit for protection against larger negative voltages. The technical effect of this patent is to provide a reliable and efficient way to protect thyristors from damage caused by excessive voltage spikes.

Problems solved by technology

At some voltage, the electric field at the J2 junction grows so strong that the J2 junction starts to breakdown and a small amount of avalanche current begins to flow, but the amount of current is not adequate to turn on transistor 5.

The thyristor can, however, be switched off if an external circuit momentarily causes the anode to be negatively biased with respect to the cathode.

Very large and expensive thyristors are used to switch high voltages in high power applications.

If the magnitude of the high voltage DC were to momentarily pulse high, such as due to the power line being struck by lightning, then an intolerably high transient voltage might be momentarily placed across the thyristor stack (the anode voltage is at too high a positive voltage with respect to the cathode), causing excessive current flow through the stack if the thyristors were on, and causing localized overheating and failure of the stack.

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