| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a power factor improving circuit capable of controlling the circuit stably while decreasing the number of wiring lines, and to provide a power supply. <P>SOLUTION: The power factor improving circuit comprises a resistor Rsh for detecting a current flowing through an AC power supply Vac, a rectifier circuit B or a switch Q1, a section H for creating a control voltage proportional to the output voltage Eo, and a control circuit 10a operating with the control voltage as the power supply voltage. The control circuit comprises an output voltage detecting operational amplifier 11 for amplifying the error between the control voltage from the control voltage creating section and a predetermined reference voltage to create an error voltage, a variable gain amplifier 15 for amplifying a voltage proportional to a current detected by the current detecting resistor by making the gain variable depending on the error voltage level, and a pulse width modulator 14 for creating a pulse signal by controlling the pulse width depending on the output level from the variable gain amplifier and controlling the output voltage to a predetermined level by applying that pulse signal to the switch Q1. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
