| 摘要 |
PROBLEM TO BE SOLVED: To prevent malfunction and destruction of a switching element by properly setting a blanking period of a switching power supply unit. SOLUTION: The switching power supply unit 1 of this invention includes a switching current detecting circuit 9 detecting the amount of current flowing a switching element 8 and a control circuit 3 generating a control signal of the switching element 8 based on the detected voltage provided by the circuit 9 and a converted input voltage V<SB POS="POST">i</SB>. The control circuit 3 includes an oscillation circuit 21 which outputs a signal oscillating between a first state and a second state. The control circuit 3 turns on the switching element 8 until a predetermined blanking period elapses from the moment that the output of the oscillation circuit 21 changes from the second state to the first state and turns off the switching element 8 when the detected voltage exceeds a predetermined target voltage after the blanking period elapsed. Further, the control circuit 3 sets a long blanking period when the converted input voltage is high and sets a short blanking period when the converted input voltage is low. COPYRIGHT: (C)2012,JPO&INPIT |
