| 摘要 |
PURPOSE:To prevent breakdown of thyristor due to surge voltage and also prevent production of arc at contacts by associating the switching of the power source switch and the control of thyristor. CONSTITUTION:When a control terminal a is input with control signals, a transistor 17 is powered for operating a relay 18 so as to close a contact 5. Then signals delayed by a delay circuit 14 reach a point b and thereby a transistor 19 is powered for operating a relay 20 so as to close a contact 6. A thyristor 3 is continued with a necessary phase for supplying electric power which is phase controlled by a load 4. If the control signals are removed from the control terminal a, the contact 6 opens for discontinuing the thyristor 3. Therefore, the contact 5 also opens and thereby the circuit is broken off completely. |
