Patent ID: 6580624
Filing Date: 2003-06-17
Classification: H02M

Abstract:
A switching power circuit, comprising:a first rectification circuit for rectifying an alternating current power so as to generate a first pulsating voltage; a noise filter for controlling a noise of a switching frequency, said noise filter including a coil and a condenser configured as an LC filter connected across said first pulsating voltage, wherein said condenser is other than a smoothing condenser connected directly to said first rectification circuit; a switching circuit for controlling ON/OFF of said first pulsating voltage based on a control signal which is input so as to generate a first alternating current voltage having a predetermined frequency higher than a frequency of said alternating current power and having a pulse width corresponding to said control signal; a transforming circuit for transforming said first alternating current voltage so as to generate a second alternating current voltage of a predetermined voltage value; a second rectification circuit for rectifying said second alternating current voltage so as to generate a second pulsating voltage; a smoothing circuit for smoothing said second pulsating voltage so as to generate a direct current voltage and for applying said direct current voltage to a load, wherein said smoothing circuit comprises an electrical double layer condenser of which a volume per unit capacity is smaller than that of an aluminum electrolytic condenser, and of which an impedance is set under 1% of a load impedance; a voltage change detecting circuit for detecting a change of said direct current voltage in a period longer than a period of a ripple included in said direct current voltage so as to generate a detection signal; and a control circuit for generating said control signal used to execute a negative feed-back control of said pulse width of said first alternating current voltage based on a level of said detection signal.