Voltage limiter circuit

Claim 2

In a circuit which includes a node, a plurality of current paths connected in parallel between said node and a point of reference potential, at least some of said paths each including at least one semiconductor junction poled in the same sense relative to said node, and in which there is produced at said node a voltage which may, at times, be in the reverse direction relative to said junctions and which, if not limited, may reach a level such as to adversely affect the circuit operation by causing reverse breakdown of one or more of said junctions, the improvement comprising: one of said paths exhibiting a substantially lower resistance than all of the others to a voltage at said node in said reverse direction which attempts to exceed a given value, said path including one of said semiconductor junctions which will tolerate reverse breakdown without adversely affecting circuit operation, that junction having a substantially lower reverse breakdown voltage than the junctions in said other paths, whereby any tendency of said reverse voltage at said node to increase beyond said given value results in non-destructive current flow in the reverse direction through said junction to thereby limit the voltage at said node; an inductor connected between said node and said point of reference potential; and said one junction comprising the base-to-collector electrode junction of a transistor which has also a base-to-emitter electrode junction, said transistor being connected to said node at said emitter electrode.

Claim 3

In a circuit as set forth in claim 1, further including: means responsive to a trigger pulse for supplying current in the forward direction through the collector-to-emitter electrode path of said transistor to said inductor and for terminating the flow of said current after an interval of time, whereby after termination of said flow of current, the voltage across said inductor reverses and the voltage at said node, which is now in the reverse direction relative to said base-to-collector electrode junction, causes the flow of current in the reverse direction through said base-to-collector junction.

Claim 4

In a circuit which includes a node, a plurality of current paths connected in parallel between said node and a point of reference potential, at least some of said paths each including at least one semiconductor junction poled in the same sense relative to said node, and in which there is produced at said node a voltage which may, at times, be in the reverse direction relative to said junctions and which, if not limited, may reach a level such as to adversely affect the circuit operation by causing reverse breakdown of one or more of said junctions, the improvement comprising: one of said paths exhibiting a substantially lower resistance than all of the others to a voltage at said node in said reverse direction which attempts to exceed a given value, said path including one of said semiconductor junctions which will tolerate reverse breakdown without adversely affecting circuit operation, that junction having a substantially lower reverse breakdown voltage than the junctions in said other paths, whereby any tendency of said reverse voltage at said node to increase beyond said given value results in non-destructive current flow in the reverse direction through said junction to thereby limit the voltage at said node, said one current path including a first semiconductor region of one conductivity type, a second semiconductor region of opposite conductivity type, at one portion of the surface of said one region and within said first region and forming with said first region said one of said semiconductor junctions, a connection from said second region to said node, and a connection from said first region to said point of reference potential, and in which there is present at another portion of the surface of the first region, in only said one current path, a semiconductor region of the same conductivity type as said first region with a substantially higher concentration of impurities than in the bulk of said first region to thereby make said another portion of the surface of said first region in said one path more highly doped than the bulk of said first region in said one path, said surface region serving to lower the reverse breakdown voltage of said junction between said first and second regions in said one of said paths.

Claim 5

In a circuit which includes a node, a plurality of current paths connected in parallel between said node and a point of reference potential, at least some of said paths each including at least one semiconductor junction poled in the same sense relative to said node, and in which there is produced at said node a voltage which may, at times, be in the reverse direction relative to said junctions and which, if not limited, may reach a level such as to adversely affect the circuit operation by causing reverse breakdown of one or more of said junctions, the improvement comprising: one of said paths exhibiting a substantially lower resistance than all of the others to a voltage at said node in said reverse direction which attempts to exceed a given value, said path including one of said semiconductor junctions which will tolerate reverse breakdown without adversely affecting circuit operation, that junction having a substantially lower reverse breakdown voltage than the junctions in said other paths, whereby any tendency of said reverse voltage at said node to increase beyond said given value results in non-destructive current flow in the reverse direction through said junction to thereby limit the voltage at said node, said one current path including a first semiconductor region of one conductivity type, a second semiconductor region of opposite conductivity type, at one portion of the surface of said one region and within said first region and forming with said first region said one of said semiconductor junctions, a connection from said second region to said node, and a connection from said first region to said point of reference potential, and in which there is present at another portion of the surface of the first region, in only said one current path, a semiconductor region of the same conductivity type as said first region with a substantially higher concentration of impurities than in the bulk of said first region to thereby make said another portion of the surface of said first region in said one path more highly doped than the bulk of said first region in said one path, said surface region serving to lower the reverse breakdown voltage of said junction between said first and second regions in said one of said paths.

Claim 6

In a circuit as set forth in claim 3, said only one of said paths including as the connection between said node and said second region, a third region at the surface of said second region and within said second region, said third region being of the same conductivity type as said first region and forming a junction with said second region, said first, second and third regions comprising the collector, base and emitter electrodes, respectively, of a transistor.