Solid-state on delay time delay apparatus

Claim 1

On delay time delay apparatus comprising, in combination, first lead means adapted to be connected to one side of a single phase alternating current line, second lead means adapted to be connected to the other side of said single phase alternating current line, a full-wave rectifier having one input terminal thereof directly connected to the second lead means, the fullwave rectifier being adapted to have the other input terminal thereof connected by way of a relay coil to the first lead means, a normally nonconductive controlled rectifier having the anodecathode path thereof connected across the output leads of the full-wave rectifier and while conductive providing a closed switch whereby sufficient current from the alternating current line flows through the relay coil to actuate the relay, a small current insufficient to actuate the relay flowing through the relay coil before the controlled rectifier is gated-on, an R-C timing circuit including in series a first resistor, a timing capacitor and an adjustable timing resistor connected across the output of the full-wave rectifier, a trigger circuit including a pair of complementary NPN and PNP transistors, each of the transistors having a base, emitter and collector, the base of the PNP transistor being connected to the junction between the timing capacitor and the timing resistor and to the collector of the NPN transistor and the collector of the PNP transistor being connected to the base of the NPN transistor and by a resistance to the cathode of the controlled rectifier, the emitter of the NPN transistor being connected to the control element of the controlled rectifier to supply a gating signal thereto when the complementary transistors are conductive, the threshold level at which the complementary transistors become conductive being established by threshold level determining circuit means including in series a first Zener diode, a first diode rectifier, the emitter-base junction of the PNP transistor and a second resistor connected from the junction between the first Zener diode and the first diode rectifier to the cathode of said controlled rectifier, the last named circuit means being connected in parallel with the timing capacitor, said timing capacitor being normally discharged at the connecting moment when the first lead means and the second lead means are first connected to the alternating current line whereby the complementary transistors are nonconductive and no gate signal is supplied to the controlled rectifier thereby providing that the controlled rectifier is nonconductive, the connection of the first lead means and second lead means to the single phase alternating current line causing a small current to flow through the relay coil and the second lead means into the full-wave rectifier and to develop a full-wave rectified direct current output voltage thereacross, said full-wave rectified output current flowing through the first resistor and starting to flow into said timing capacitor, said timing capacitor after a preselected time interval being charged to a sufficient voltage to equal the threshold voltage as determined by the threshold level determining circuit means and causing the complementary transistors to conduct thereby causing the trigger circuit to supply a gating signal to the controlled rectifier, the gating signal causing the controlled rectifier to assume a conductive condition thereby causing a relay-actuating current to flow through the relay coil, resistance circuit means including third and fourth resistors both having one end thereof operatively connected to the first lead means, said third resistor having the other end thereof operatively connected to the anode of the controlled rectifier, said fourth resistor having the other end thereof operatively connected to the cathode of the controlled rectifier, said resistance circuit means obtaining a pulsating direct current with a substantially 90 electrical degree phase difference with respect to the current in the relay coil and applying said pulsating direct current to the controlled rectifier whereby current through the controlled rectifier never decreases below its holding current and the controlled rectifier is maintained in a conductive condition with full actuating current through the relay coil until the electrical circuit is broken at the first and second lead means.