Over-current protection for an alternating current circuit including automatic reset

Claim 2

An overcurrent protective circuit comprising, a first and a second terminal to be connected to a source of electrical supply: a load; a normally open switching element; a current sensing element; a connection from said first terminal through said load and through said current sensing element to said other terminal; said switching element being connected in shunt with said current sensing element; delay means for closing said switching element to bypass said current around sensing element after a short delay; and means responsive to a predetermined voltage appearing across said current sensing element to inhibit closing of said switching element by said delay means whereby the current flowing through said load is reduced when the voltage across a said current sensing element due to the current flow therethrough reaches said predetermined value.

Claim 3

The invention as expressed in claim 1 in which alternating current is applied to said terminals.

Claim 4

The invention as expressed in claim 1 in which alternating current is applied to saId terminals and in which a second switching means is connected across said first switching means, said two switching means being unidirectionally conductive and being oppositely poled and in which means are provided to render the two switching means conductive during alternate half cycles of said alternating current supply source.

Claim 5

The invention as expressed in claim 1 in which a third switching means is connected between said load and said current sensing means and in which means are provided to open said third switching means in response to said predetermined voltage appearing across said current sensing means.

Claim 6

An overcurrent protective circuit comprising: a pair of terminals to which an alternating current supply may be connected; a load; a first and a second switching means; a current sensing means; means for connecting a first one of said terminals through said load, said first switching means and said current sensing means in series to the other of said pair of terminals; means to connect said second switching means across said first switching means and said current sensing means in series; means for causing conduction of said second switching means after a period of delay after a beginning of a first half of a cycle of the alternating current applied to said terminals, whereby the current flowing through said current sensing means in a measure of the current flowing in said load during the period of said delay; and means to inhibit the conduction of said first and second switching means responsive to the voltage across said current sensing means arriving at a predetermined voltage during said delay period, whereby the supply circuit for said load is broken if the current flow therethrough is above a predetermined amount during said delay period.

Claim 7

An overcurrent protective circuit comprising: a pair of terminals to which an alternating current supply may be connected; a load; a first and a second switching means; a current sensing means; means for connecting a first one of said terminals through said load, said first switching means and said current sensing means in series to the other of said pair of terminals; means to connect said second switching means across said first switching means and said current sensing means in series; means for causing conduction of said second switching means after a period of delay after a beginning of a first half of a cycle of the alternating current applied to said terminals, whereby the current flowing through said current sensing means in a measure of the current flowing in said load during the period of said delay; and means to inhibit the conduction of said first and second switching means responsive to the voltage across said current sensing means arriving at a predetermined voltage during said delay period, whereby the supply circuit for said load is broken if the current flow therethrough is above a predetermined amount during said delay period.

Claim 8

The invention as expressed in claim 5 in which said second switching means is a silicon controlled rectifier.

Claim 9

The invention as expressed in claim 5 in which said first switching means comprises at least one transistor and means are provided to bring the base of said transistor substantially to zero potential upon said predetermined voltage appearing across said current sensing means.

Claim 10

The invention as expressed in claim 7 in which said last mentioned means comprises a third switching means.

Claim 11

The invention as expressed in claim 5 in which a fourth switching means is provided, said second and fourth switching means having rectifying properties and in which means are provided responsive to current flow in said load during a first half of a cycle to cause conduction of said fourth switching means during the second half of said cycle.

Claim 12

An overcurrent protective means comprising: a load; a current sensing means; a pair of terminals to be connected to a source of alternating current; means for passing at least a portion of the current flowing from one of said terminals to the other of said terminals through said load and also through said current sensing means for a small portion of an alternating current cycle; means for shunting the current passing through said load around said current sensing means for the remainder of said cycle; and means responsive to the current flowing through said current sensing means arriving at a predetermined level to break the circuit for the load whereby the flow of current through said load is prevented.

Claim 13

An overcurrent protective means comprising: a load; a current sensing means; a pair of terminals to be connected to a source of alternating current; means for passing at least a portion of the current flowing from one of said terminals to the other of said terminals through said load and also through said current sensing means for a small portion of an alternating current cycle; means for shunting the current passing through said load around said current sensing means for the remainder of said cycle; and means responsive to the current flowing through said current sensing means arriving at a predetermined level to break the circuit for the load whereby the flow of current through said load is prevented.