Apparatus for protecting semiconductor devices utilizing a time-varying reference signal

Claim 2

Apparatus as set forth in claim 1 wherein said feedback signal varies as a function of the current drawn by said load.

Claim 3

In a control for an electrical load in which said load is supplied with current through a gated semiconductor current-switching device for controlling the energization of said load and in which said device is selectively provided with gating current for rendering said device conductive thereby to energize said load, apparatus for protecting said device comprising: transformer means responsive to conduction of said gated semiconductor switching device for providing a feedback signal which varies as a function of an operating parameter related to the heating of said gated semiconductor current-switching device, and means controlled by said feedback signal including a relay having contacts for cutting off said gating current if the value of said parameter exceeds a desired limiting value, whereby said device is prevented from being operated in an undesired mode.

Claim 4

In an on-off control for a selectively energizable load in which said load is supplied with current through a gated semiconductor current-switching device for controlling the energization of said load and in which said device is selectively provided with gating current for rendering said device conductive thereby to energize said load, apparatus for protecting said device comprising: means for providing a feedback signal which varies as a function of an operating parameter related to the heating of said device; means for providing a reference signal which represents a desired limiting value of said parameter; and means controlled by said feedback and reference signals for cutting off said gating current if the value of said parameter exceeds said desired limiting value whereby said device is prevented from being operated in an undesired mode.

Claim 5

In an on-off control for an electric motor in which said motor is supplied with current through a gated semiconductor current-switching device for controlling the energization of said motor and in which said device is Selectively provided with gating current for rendering said device conductive thereby to energize said motor, apparatus for protecting said device comprising: means for providing a feedback signal having an amplitude which varies as a function of the current drawn by said motor; means for generating a time-varying reference signal the amplitude of which is an analog of the current-carrying capability of said device; and means for cutting off said gating current if the instantaneous amplitude of said feedback signal exceeds the instantaneous amplitude of said reference signal whereby said device is prevented from being overloaded.

Claim 6

Apparatus as set forth in claim 6 wherein said feedback signal providing means includes a current transformer responsive to current drawn by said load.

Claim 7

Apparatus as set forth in claim 7 wherein said feedback signal providing means further comprises rectifier means for converting an AC signal obtained from said current transformer to a DC feedback signal.

Claim 8

Apparatus as set forth in claim 6 wherein said reference signal generating means comprises a capacitor and means for discharging said capacitor at a predetermined rate.

Claim 9

Apparatus as set forth in claim 6 wherein said reference signal generating means comprises a capacitor and means operative upon initial energization of said motor for discharging said capacitor at a predetermined rate.

Claim 10

Apparatus as set forth in claim 10 wherein said means for discharging said capacitor includes a Schmitt trigger circuit responsive to current drawn by said motor for initiating discharging of said capacitor.

Claim 11

Apparatus as set forth in claim 11 wherein said means for discharging said capacitor further comprises a resistor and an SCR for selectively connecting said resistor across said capacitor and wherein said SCR is triggered by said Schmitt trigger circuit.

Claim 12

Apparatus as set forth in claim 12 including a second SCR for applying the voltage on said capacitor to said means for cutting off said gating current and wherein said second SCR is triggered by said Schmitt trigger circuit.

Claim 13

Apparatus as set forth in claim 6 wherein said feedback and reference signals are DC voltages and wherein said means for cutting off said gating current includes a sense amplifier responsive to the relative amplitudes of said feedback and reference signals.

Claim 14

Apparatus as set forth in claim 14 wherein said means for cutting off said gating current comprises a relay having contacts for controlling said gating current and a semiconductor controlled rectifier for controlling the energization of said relay and wherein said sense amplifier controls the gating of said rectifier.

Claim 15

Apparatus as set forth in claim 6 wherein said motor is a three-phase AC motor and wherein current is supplied to each phase thereof through a triac.