| 摘要 |
PURPOSE:To prevent destruction of the high frequency electric power supply circuit side caused by a change in impedance of an excitation coil contained load circuit when lighting is transitional. CONSTITUTION:When lighting of an electrodeless lamp is transitional, since an oscillation signal 60 is inputted to a drive circuit 1 from a VCO13, FETs 2 and 3 output a high frequency current having the same frequency with the oscillation signal 60 to a load circuit on the excitation coil 5 side. In this condition, a phase detecting circuit 11 inputs the high frequency current flowing to the load circuit and high frequency voltage impressed upon the load circuit through a CT4 and capacitors C1 and C2, and outputs equivalence produced when a phase difference between these voltage and electric current becomes different from prescribed phase difference to an adder 20 as phase detection voltage. The VCO13 changes frequency of the oscillation signal 60 in a direction that the phase detection voltage added to reference voltage by the adder 20 becomes (0). Thereby, the phase difference between the high frequency voltage and the electric current supplied to the load circuit is controlled to be almost constant in spite of a change in load side impedance. |
