| 摘要 |
PURPOSE:To improve the rapidness by commonly using an overcurrent detecting resistor at the low voltage side of a switching element and a voltage divider, and connecting it between it and the low voltage side of a reference voltage, thereby improving the voltage variation rate. CONSTITUTION:A DC voltage Ein is applied to a switching control circuit 101 to control ON and OFF its switching element 4, and the voltage of the secondary side coil S of a transformer 5 is supplied through a rectifying and smoothing unit 103 to a load RL. In this case, an overcurrent detecting resistor 16 inserted as a bias resistor between the base and the emitter of a transistor (Tr) in an overcurrent protecting circuit 12 is provided between the ground point of a reference voltage circuit 112 and Trs 14, 15 and the low voltage common connecting point of the element 4 and a voltage divider 111. Thus, the resistor 16 becomes a bias resistance between the base and the emitter of the protecting circuit 12, and turns ON the Tr15 when becoming the overcurrent to suppress the output of the element 4 and simultaneously superposes the voltage variation directly on the current variation. |
