| 摘要 |
A first feedback path is connected across one of the commutating reactive components of an induction cooking unit chopper inverter for deriving a first high frequency alternating current gate controlling signal voltage at substantially the operating frequency of the chopper-inverter. A second feedback path is connected to the high voltage power supply terminals for deriving a second alternating current gate controlling signal voltage at the frequency of the high voltage potential appearing across the high voltage power supply terminals including the low frequency, undulating, full wave rectified 120 hertz excitation potential component supplied by the full wave rectifier bridge. A gating signal generator is provided for deriving high frequency output gating signal pulses of sufficient magnitude to assure safe turn-on of the power rated thyristor and is energized from the low voltage direct current power supply. A first control switch is coupled to and enables operation of the gating signal generator and includes a direct current bias circuit supplied from the low voltage direct current power supply for supplying direct current bias potential to the first control switch. A common alternating current coupling path comprising a differentiating circuit supplied with both the first feedback high frequency alternating current gate controlling signal voltage and the second feedback alternating current gate controlling signal voltage, differentiates the two feedback gate controlling signals and supplies the differentiated output in common to the first control switch to control operation of the first control switch in conjunction with the direct current bias potential. The circuit arrangement provides zero point switching during initial turn-on of the thyristor at or near the zero point of the high voltage full wave rectified excitation potential supplied across the high voltage power supply terminals, and both unity power factor and unity form factor operation whereby sinusoidal line current is drawn for all values of loading from no-load to full-load and without requiring substantial supply line filtering components. |
