| 摘要 |
PURPOSE:To eliminate a voltage dividing circuit of high withstand voltage and high accuracy from a synchronous detecting circuit, and lower cost by constituting the synchronous detecting circuit in such a way as capable of generating a synchronous signal based upon voltage generated in a search coil wound around a magnetic core forming a part of a magnetic circuit laid in the vicinity of a heating coil. CONSTITUTION:When a switching element 6 is actuated with a pulse signal from a PWM modulator 12 via a driver 13 and an inverter 5 is thereby caused to start operation, rectified and smoothing current supplied to the inverter 5 is cyclically switched on and off, and converted into a high frequency of several tens of hundreds Hz. This high frequency is applied to a heating coil 4 for the induction heating of a pan. In this case, voltage waveforms of several volts easy to be processed with a comparator 16 are generated by the search coil 14, depending upon a switching waveform applied to the coil 4. The generated voltage waveforms are compared in the comparator 16. Then, the rising edge of the waveform is detected with a differentiating circuit 22 on the basis of output from the comparator 16, thereby generating a synchronous signal. This synchronous signal is used to keep synchronous state with the pulse signal from the modulator 12 for driving the element 6. Thus, a switching loss is restrained to low level, and good switching operation is performed. |
