| 摘要 |
PURPOSE:To obtain a TV constant voltage power circuit which features the low cost, the quick response speed and the small power consumption each by extending more the period during which the switch circuit connected to the control transformer is short-circuited in the H period as the boosting voltage decreases. CONSTITUTION:The switch circuit comprising D14 and control transistor Tr15 is connected to the secondary wiring of control transformer 13 connected in series to boosting diode D10. When the voltage of boosting capacitor C11 is going to be less than the reference voltage, the pulse duration generated from mono-multi 16 increases with reduction of the collector current of Tr21. As a result, both the saturation time of Tr15 and the short-circuit time of the secondary wiring of transformer 13 are increased, and then the average current of D10 increases to try to heighten the voltage of C11. When the voltage of C11 is going to be more than the reference voltage, the contrary action is given to lower the C11 voltage automatically. Thus, the boosting voltage is stabilized. Accordingly, the rating of control Tr can be utilized effectively to realize the low cost by selecting properly the ratio between the 1st and 2nd wirings sence the transformer is used as the current control element. |
