System for detecting faulty SCR's

Claim 2

In a load current controller of the type in which triggerable semiconductor current control elements are disposed in series relation between an alternating current source and a load and having means for adjusting the firing angle of said semiconductor current control elements, apparatus for sensing a short circuit failure of said semiconductor current control elements, comprising: (a) means for sensing the level of current flowing from said source of alternating current through said load; and (b) means coupled to said sensing means for signaling the existence of a predetermined non-zero current in the load at a time in the alternating current cycle prior to the triggering of said semiconductor current control elements when no load current should be present.

Claim 3

A load current controller apparatus, comprising: (a) at least one silicon controlled rectifier, having an anode electrode, a cathode electrode and a gate electrode, said anode and cathode electrodes adapted to be connected in series between alternating current supply terminals and a load whose current is to be controlled; (b) means adapted to be coupled to said alternating current supply terminals for generating a ramp voltage signal synchronized with the alternating current supply; (c) means for comparing said ramp voltage signal to a predetermined set-point reference voltage, said comparing means providing an output voltage when the ramp voltage exceeds said set-point reference voltage; (d) toggling means for successively and alternately coupling said comparator output voltage to said gate electrode of said silicon controlled rectifier; (e) means for sensing the level of current flowing through the load; and (f) means coupled to said sensing means for indicating the existence of load current prior to the instant that said comparator output voltage is produced.

Claim 4

A load current controller apparatus, comprising: (a) at least one silicon controlled rectifier, having an anode electrode, a cathode electrode and a gate electrode, said anode and cathode electrodes adapted to be connected in series between alternating current supply terminals and a load whose current is to be controlled; (b) means adapted to be coupled to said alternating current supply terminals for generating a ramp voltage signal synchronized with the alternating current supply; (c) means for comparing said ramp voltage signal to a predetermined set-point reference voltage, said comparing means providing an output voltage when the ramp voltage exceeds said set-point reference voltage; (d) toggling means for successively and alternately coupling said comparator output voltage to said gate electrode of said silicon controlled rectifier; (e) means for sensing the level of current flowing through the load; and (f) means coupled to said sensing means for indicating the existence of load current prior to the instant that said comparator output voltage is produced.

Claim 5

Apparatus as in claim 2 wherein said means for sensing the level of load current flowing through said load comprises: (a) current responsive means adapted to be operatively coupled between said alternating current source terminals and said load; (b) a bistable circuit having a first input, a second input coupled to the output of said comparing means, and an output terminal; and (c) means coupling said current responsive means to said first input of said bistable circuit.

Claim 6

Apparatus as in claim 2 wherein said toggling means comprises: (a) first and second gated amplifiers, each having a signal input, an enable input and an output; (b) means coupling the output voltage of said comparing means to said signal input of each of said gated amplifiers; (c) a toggle flip-flop having a toggle input terminal and true and complement output terminals; (d) means coupling said toggle input terminal to a source of toggling pulses; and (e) means coupling the enable input of said first and second gated amplifiers to said true and complement output terminals of said toggle flip-flop, respectively.