| 摘要 |
PROBLEM TO BE SOLVED: To obtain a switching power supply that allows a switching transistor using MOSFET to be actuated and operated with reliability even on low input voltage, and offers high efficiency over a wide range of input voltage. SOLUTION: An auxiliary transistor Q4 is connected between the point B of connection between the gate of a first switching transistor Q1 and the collector of a second switching transistor Q2, and earth. A capacitor C4 is connected between the point A of connection between the first switching transistor Q1 and primary winding N1, and the base of the auxiliary transistor Q4, and a resistor R7 is connected between the point B of connection and the base of the transistor Q4. When the circuit is actuated, the auxiliary transistor Q4 is turned on by the resistor R7, and the gate potention of the first switching transistor Q1 is thereby reduced. As a result a voltage higher than the minimum driving voltage between the gate and source of the MOSFET is obtained. |
