| 摘要 |
PROBLEM TO BE SOLVED: To obtain a desired output voltage with small-sized electric and electronic elements by comprising a PWM control circuit of a peak voltage detecting circuit, a subtracting circuit, a comparator circuit, a PWM oscillation circuit, and a driving circuit. SOLUTION: The voltage from an AC power source E1 is divided by means of voltage dividing resistors R4 and R5 after the voltage is rectified by means of a rectifier DS, and an operational amplifier IC1, a diode D2, and a capacitor C2 detect and hold the peak voltage, but the value of the detected peak voltage becomes proportional to the peak voltage of the power source E1. The peak voltage is outputted to a subtracting circuit 20 as a reference peak voltage, and the circuit 20 performs subtraction on the voltage and outputs the subtracted result to a comparator circuit 30 which compares the subtracted result with the voltage of a reference voltage generating circuit 40. When a boosted voltage is controlled so that the voltage can become constant, the relationship between the input voltage Vi and the final output voltage V0 of the power source E1 is fixed and, when the difference is made smaller, the withstand voltage of a poststage element can be maintained at the conventional value. In addition, the size and loss of a power factor improving circuit can be reduced, because the burdens to a choke coil L1 and a transistor Q1 can be reduced. |
