High-voltage scr circuit for microwave oven and the like

Abstract

An SCR circuit is provided in a high-voltage supply for energizing a magnetron that is assembled in a microwave oven. The high-voltage supply circuit includes a voltage step-up transformer. This transformer is arranged with a low-voltage secondary winding which is connected across the heater-cathode electrode of the magnetron and a high-voltage secondary winding which is coupled in series with a capacitor. The series combination of the capacitor and the high-voltage secondary is connected across the cathode and anode electrodes of the magnetron; and importantly, the high-voltage SCR circuit includes a number of series-connected SCR's electrically in shunt of the magnetron. A triggering circuit gates the high-voltage SCR circuit to the current-conducting state during a selected phase portion of an applied AC potential, in order to control the amount of power being supplied to the magnetron. The high-voltage SCR circuit also advantageously includes a diode and a coil disposed in electrical series with the series-connected SCR's respectively to cooperate with the SCR's in blocking reverse voltage and to limit the rate of current rise in the forward direction. A coupling circuit is associated with the gate terminal of each of the individual SCR's for coupling the triggering circuit gating signal to all of the SCR gates simultaneously, while preventing current leakage back through the coupling circuits.