| 摘要 |
PROBLEM TO BE SOLVED: To prevent operation efficiency of a power supply device from decreasing, by prolonging the time of on-state of a switching element even if the load current of a transformer decreases in a power saving mode.SOLUTION: A power supply device includes a transformer 107 having a primary winding Np, a second winding Ns and auxiliary windings Nb, Nb2, an FET 108 for turning current supply to the primary winding of the transformer on/off, a current detection resistor 111 which detects a current flowing through the primary winding, and outputs a voltage dependent on the current, a switching control IC 106 which controls the FET on/off depending on a voltage output from the current detection resistor, and a current detection circuit 209 for detecting a current flowing through the auxiliary winding Nb2 having the same winding direction as that of the primary winding of the transformer, and a resistance voltage division circuit 210 which switches the voltage value being output to the switching control IC by the current detection resistor if the current flowing through the auxiliary winding Nb2 exceeds the predetermined value, so as to be smaller than the voltage value before exceeding the predetermined value. |
