| 摘要 |
<p>PURPOSE: To make possible improving a power factor using simple circuit constitution, to make possible producing a DC source voltage without increasing the size of a power transformer, and to feed electricity to a backlight well. CONSTITUTION: An alternating current from an AC power supply is voltage- transformed at a predetermined level by a power transformer 2 and supplied to a feeder circuit for a backlight and to a DC feeder circuit. The alternating current supplied is converted into a direct current by a first rectifying smoothing circuit 3 to produce a DC voltage and applied to a Zener diode 5. The AC is also converted into DC voltage by a second rectifying smoothing circuit 6 and applied to an external circuit. A Zener diode 5 is turned on or off according to the value of the current applied, thus controlling the switching action of switching elements Q1, Q2. Therefore, electricity is fed to the DC feeder circuit during the period of a phase near the peak value of th input current, and is fed to the backlight 4 during the period of a phase other than the peak value. Thus a circuit which feeds electricity to the backlight and feeds direct current using one power transformer can be formed without increasing the size of the power transformer 2, and the power factor of the entire circuit can be improved to a large extent.</p> |
