| 摘要 |
At the initiation of each successive waveform of a train of positive polarity stepped waveforms, a first single-pole-single-throw (SPST) switching circuit is operated for applying this train of waveforms across a fullwave SCR bridge mixer network having individual diodes connected in inverse parallel across each SCR. For alternating ones of the train of waveforms, a different diagonal pair of SCR's of the mixer are turned on at the initiation of an associative waveform, for supplying alternating current to and a dual polarity AC voltage across a load. At the end of the period of each waveform, the first switching circuit is operated for removing the train of waveforms from the mixer, and thereafter a second switching circuit is operated for applying a negative voltage across the mixer network, causing the diodes to become forward biased for reverse biasing their respective SCR's, thereby turning off the conducting ones of the SCR's via natural commutation. More than one diode is connected in a series circuit, and the series combination connected in inverse parallel with each SCR, for substantially reducing the turnoff times of the SCR's. After the SCR's turn off, the second switching circuit is operated for disconnecting the negative voltage from the mixer network prior to the initiation of the next waveform.
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