| 摘要 |
Electrical switching device for controlling current now from an alternating current source (10) and having a main thyristor (14, 16) such as a triac or a silicon controlled rectifier connected in series with a load (12) across the source. The control terminal (14c, 16c) of the thyristor (14, 16) is coupled via a diac (30) to a control signal generating circuit (18) operable to vary the conduction interval of the thyristor (14, 16) on each cycle of voltage from the supply (10) by switching the diac (30). A further thyristor (38, 42) such as a triac or silicon controlled rectifier is connected to be responsive to the switching of the diac (30) to be itself switched so as to provide a current now path from the control terminal (14c, 16c) of the main thyristor to render the main thyristor insensitive to immediate further control under influence of the diac. |
