| 摘要 |
PURPOSE:To reduce the electric loss of a constant voltage switching element by connecting a rectifying element and the primary side of a transformer in series, turning on and off the secondary side of the transformer through a switch, and thus controlling the time width of a current flowing to a load side. CONSTITUTION:The ratio of the primary winding N1 and secondary winding N2 of a transformer T2 is set to 1:10. When a voltage across a load 2 is high, a constant voltage control circuit 6 which synchronises with an input voltage supplied from a synchronizing signal line 5 extends the off time of a transistor switch TR2 to reduce the time width of a current flowing through the load 2, and when low, the time width of the current flowing through the load 2 is increased, thus holding the load voltage constant. Therefore, when the TR2 is turned off, impedance viewed from the primary side of the transmformer T2 is large and a little load current flows and when on, a voltage drop across the T2 is one tenth as large as the sum of the voltage of a diode D2 for reverse current prevention and the saturation voltage of the TR2, so it is very small. |
