| 摘要 |
PURPOSE:To simplify a trigger circuit in a switching circuit by commonly connecting one end of a gate trigger element to one output end of a DC power source circuit, and operating a logic circuit element in response to the gate trigger element to generate a gate signal. CONSTITUTION:When a high level signal is produced from a control circuit 19, the output of an AND gate 17 becomes high level, a transistor 22 is conducted to thus conduct a gate trigger element 2. Accordingly, the output of an OR gate 14 becomes low level to decrease the output of the AND gate 17 and to turn OFF the transistor 22. When the gate trigger element 2 is turned OFF at the zero cross position of an AC power source 1, the output of the OR gate 14 become high level, one input of the AND gate 17 gradually increases. When it reaches a predetermined level, the output of the AND gate 17 becomes high level to conduct the transistor 22 and thereby conduct the gate trigger element 2. |
