| 摘要 |
The system includes a control unit (1) for supplying a load (10,11,12) and a processing unit (2) connected to the control unit (1). The system has means for determining the polarity of a supply voltage between supply feeds (5,7) and the processing unit (2) and has a switch (17), connected at its output terminals to the processing circuit (2), which is controlled by an intermittent half waveform having two polarities so as to reduce an average supply voltage (v) supplied to the load. The processing circuit controls the closing of the switch (17) by using a pre-determined number (21,22) of half waves during a cycles having an odd number of consecutive half waves (21,22,23,g1,g2,g3). The system has an opto-coupler (15) whose input diode is connected through a resistance (16) between the supply lines (5,7). The outputs of the opto-coupler are connected to the inputs of the processing circuit to provide signals representing the half wave polarities of the voltage. The load is controlled by the triac (17), whose conduction is controlled by a second opto-coupler (18) whose output is connected in series with a resistance (19) between the trigger and anode of the triac. The opto-coupler is preferably of the type optotriac (rtm). If used as a timer with pre-set extinction the half waves suppressed during the pre-set stage do not disturb the electrical network with continuous or parasitic components.
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