| 摘要 |
A triac functions as an electronic switch to intermittently connect the AC power circuit to a load, and is directly connected to the output of a 1422 integrated circuit timer which turns the triac on and off according to a controlled cycle. The timer functions as an astable multivibrator which alternately produces high or low output voltages responsive to movement of a control voltage between high and low trigger voltage levels. A charging circuit, including a capacitor and variable resistor, is connected directly between the DC power supply and the timer input to produce an increasing control voltage; and the control voltage is discharged through the timer to produce a decreasing control voltage which determines the duty cycle. The duty cycle is variable by means of a variable resistor in the charging and discharge circuits; and the control includes calibration for the time base.
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