| 摘要 |
PROBLEM TO BE SOLVED: To maintain high power conversion efficiency for stable operation, even if input voltage fluctuates by comparing an output detection voltage with a reference one for controlling the frequency, and by providing two modes corresponding to the level of an input voltage as a reference voltage, when transferring to a transformer-driving circuit. SOLUTION: Output supplied to a load from a piezoelectric transformer is detected by a load current detection circuit 24. Also, a detection voltage is compared with a reference by an error amplifier 25, the difference is amplified, and an error voltage outputted from the error amplifier 25 is converted into frequency by an oscillator 26 for transferring to a transformer-driving circuit 21 via a switching-driving circuit 27. In this case, the reference voltage is made available in two ways by dividing a voltage V6 of a constant-voltage generator 29 with a resistor, and changing the division ratio with a transistor Tr2. More specifically, when the input signal of a terminal 31 is low, the transistor Tr2 is turned off, and the reference voltage is high, whereas when the input signal of the terminal 31 is high and the transistor Tr2 is turned on, the reference voltage becomes low. |
