Level sensing arrangement and control circuit

Claim 2

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in rEsponse to said source of alternating voltage, a trigger circuit for controlling the conduction of said control device so that said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, first control means responsive to the magnitude of current flow in said load circuit for firing said SCR when said current flow exceeds a predetermined value, means for developing an auxiliary supply voltage from said source of alternating voltage, and a light emitting diode connected between said auxiliary supply voltage and the anode of said SCR, said diode being rendered conductive when said SCR is fired, thereby to hold said SCR in a conductive state while at the same time conduction of said light emitting diode provides a visible indication that said predetermined value of current flow in said load circuit has been exceeded.

Claim 3

The combination of claim 1, wherein said trigger circuit includes a resistance - capacitance charging network for determining the point of conduction of said control device, and means connecting the anode - cathode circuit of said SCR across said charging network so that said trigger circuit is disabled when said SCR is fired.

Claim 4

The combination of claim 1, which includes second control means having a temperature sensitive resistance element and arranged to provide an output signal when a predetermined temperature value is exceeded and means responsive to said output signal for firing said SCR, thereby to disable said trigger circuit so that said output potential is no longer developed across said load circuit.

Claim 5

The combination of claim 3, wherein said second control means includes a transistor connected between said auxiliary supply voltage and said temperature sensitive element, means normally biasing said transistor to a conducting state, means for rendering said transistor nonconductive in response to an open circuit condition of said temperature sensitive element, and means controlled by said last named means for developing said output signal.

Claim 6

The combination of claim 4, which includes a second transistor, means for supplying a voltage proportional to the current flowing in said temperature sensitive element to the base of said second transistor, means connecting the collector of said second transistor to the gate electrode of said SCR, and means for adjusting the voltage supplied to the base of said second transistor so that said second transistor may be rendered conductive at a precise value of resistance of said resistance element.

Claim 7

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in response to said source of alternating voltage, a trigger circuit connected to said load circuit for rendering said control device conductive during each cycle of said alternating current source at a point in each cycle which varies in accordance with the potential across said load circuit, whereby said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, a temperature sensitive resistance element, means normally establishing a flow of unidirectional current through said element of predetermined magnitude, and level detecting means connected to the gate electrode of said SCR and responsive to the unidirectional voltage level across said resistance element for rendering said SCR conductive when current flow through said element differs from said predetermined magnitude by a predetermined amount, thereby to disable said trigger circuit and terminate development of said voltage across said load circuit.

Claim 8

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in response to said source of alternating voltage, a trigger circuit connected to said load circuit for rendering said control device conductive during each cycle of said alternating current source at a point in each cycle which varies in accordance with the potential across said load circuit, whereby said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, a temperature sensitive resistance element, means normally establishing a flow of unidirectional current through said element of predetermined magnitude, and level detecting means connected to the gate electrode of said SCR and responsive to the unidirectional voltage level across said resistance element for rendering said SCR conductive when current flow through said element differs from said predetermined magnitude by a predetermined amount, thereby to disable said trigger circuit and terminate development of said voltage across said load circuit.

Claim 9

The combination of claim 6, wherein said level detecting means includes a transistor connected between said auxiliary supply voltage and said element, means normally biasing said trAnsistor to a conducting state, means responsive to an open circuit condition of said element for rendering said transistor nonconductive, and means responsive to termination of current flow in said transistor for firing said SCR.

Claim 10

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in response to said source of alternating voltage, a trigger circuit for controlling the conduction of said control device so that said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, a temperature sensitive resistance element, means normally establishing a flow of unidirectional current through said element of predetermined magnitude, level detecting means connected to the gate electrode of said SCR and responsive to the unidirectional voltage level across said resistance element for rendering said SCR conductive when current flow through said element differs from said predetermined magnitude by a predetermined amount, thereby to disable said trigger circuit and terminate development of said voltage across said load circuit, an auxiliary supply voltage from said source of alternating voltage, and a light emitting diode connected between said auxiliary supply voltage and the anode of said SCR, said diode being rendered conductive when said SCR is fired, thereby to hold said SCR in a conductive state while providing a visible indication of the resistance value of said element.

Claim 11

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in response to said source of alternating voltage, a trigger circuit for controlling the conduction of said control device so that said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, a temperature sensitive resistance element, means normally establishing a flow of unidirectional current through said element of predetermined magnitude, level detecting means connected to the gate electrode of said SCR and responsive to the unidirectional voltage level across said resistance element for rendering said SCR conductive when current flow through said element differs from said predetermined magnitude by a predetermined amount, thereby to disable said trigger circuit and terminate development of said voltage across said load circuit, an auxiliary supply voltage from said source of alternating voltage, and a light emitting diode connected between said auxiliary supply voltage and the anode of said SCR, said diode being rendered conductive when said SCR is fired, thereby to hold said SCR in a conductive state while providing a visible indication of the resistance value of said element.

Claim 12

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in response to said source of alternating voltage, a trigger circuit for conrolling the conduction of said control device so that said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, a temperature sensitive resistance element, means normally establishing a flow of unidirectional current through said element of predetermined magnitude, level detecting means connected to the gate electrode of said SCR and responsive to the unidirectional voltage level across said resistance element for rendering said SCR conductive when current flow through said element differs from said predetermined magnitude by a predetermined amount, thereby to disable said trigger circuit and terminate development of said voltage across said load circuit, means for developing an auxiliary supply voltage from said source of alternating voltage, a transistor connected between said auxiliary supply voltage and said element, means normally biasing said transistor to a conducting state, means responsive to an open circuit condition of said element for rendering said transistor nonconductive, and means responsive to termination of current flow in said transistor for firing said SCR.

Claim 13

A control circuit, comprising a source of alternating voltage, a load circuit, means including a control device for developing an output potential across said load circuit in response to said source of alternating voltage, a trigger circuit for conrolling the conduction of said control device so that said output potential is stabilized, means including an SCR for disabling said trigger circuit so that said output potential is no longer developed across said load circuit, a temperature sensitive resistance element, means normally establishing a flow of unidirectional current through said element of predetermined magnitude, level detecting means connected to the gate electrode of said SCR and responsive to the unidirectional voltage level across said resistance element for rendering said SCR conductive when current flow through said element differs from said predetermined magnitude by a predetermined amount, thereby to disable said trigger circuit and terminate development of said voltage across said load circuit, means for developing an auxiliary supply voltage from said source of alternating voltage, a transistor connected between said auxiliary supply voltage and said element, means normally biasing said transistor to a conducting state, means responsive to an open circuit condition of said element for rendering said transistor nonconductive, and means responsive to termination of current flow in said transistor for firing said SCR.