| 摘要 |
PURPOSE:To remarkably suppress generation of noise due to a rush current with simple constitution by detecting a point of zero cross time in each phase to electrify a heating coil based on specific value detection of two phase voltages of a three-phase AC power supply. CONSTITUTION:When a start key is operated in an external key input part 26, a control part 25 of a microcomputer 19 starts a start port 27 through the first external interruption port 21 based on an input of a zero cross signal from the first zero cross detecting circuit 17, to start switching action of a transistor 6. Further, a connecting condition is decided by action of a timer 30 and the control part 25 through the port 21, and as a result to activate the first thyristor start port 31, and a thyristor corresponding to an R-phase is turned on through the first thyristor trigger circuit 32 to close an R-phase power supply to a heating coil 5 in the vicinity of zero voltage. Similarly, also S-, T-phases can be closed in the vicinity of zero voltage. |
