| 摘要 |
PURPOSE:To remove entirely danger due to short circuit on a switching element by detecting voltage among main electrodes of the switching element controlling a heating line. CONSTITUTION:When a temperature controlling circuit 11 is at a temp. t2 where the supply of power to a heating line 7 is commanded a temperature controlling output signal S1 is outputted at zero voltage of an AC power source 1 to a gate of a switching element 8 to cause the element 8 to conduct and the AC power 1 is supplied to the heating line 7 and simultaneously a synchronizing signal S3 for temperature control is inputted to a gate circuit 23. AT t6, the signal S1 stops and the element 8 turns off. Between t8-t9, despite that the S1 is not made to output, the element 8 is kept at an on-state, an AND of the gate circuit 23 is formed, the outputs becomes ''H'' to turn a protective thyristor 5 on. Hereby, resistance 4 is heated to cause a temperature fuse 3 to open and the power supply to the heat generating line 7 stops. |
