| 摘要 |
PROBLEM TO BE SOLVED: To stabilize a power-supply circuit without sharply changing a voltage supplied to a control IC by a method wherein a semiconductor element in which the inflow part of a current is connected to one end of an attenuation resistance and in which the outflow part of the current is connected to the other end is installed, the attenuation resistance is used in an overvoltage and the circuit is driven in a mode which selects the semiconductor element when a voltage is lower than a prescribed voltage. SOLUTION: When a detection voltage Vk is high in a selection and changeover circuit 14, a current supplied from an auxiliary coil Np13 flows via a resistor RD, and an attenuation voltage Vk is supplied as a voltage Vcc1 supplied to a control IC 13. When the detection voltage Vk is small, the current which is supplied from the auxiliary coil Np13 flows via a transistor Q11, and a detection voltage which is generated in the auxiliary coil Np13 is supplied as the voltage Vcc1 . In addition, in an intermediate region in which both the attenuation resistor RD and the transistor Q11 are selected, a value between the attenuation voltage Vg and the detection voltage Vk is selected. Since a voltage level to be input to a protective circuit is changed according to an increase or a decrease in an output current, an overvoltage can be protected. |
