Switching power supply device and light illuminating apparatus having the same

A switching power supply device, comprising:

• a rectifier circuit configured to rectify a commercial AC voltage to be converted into a DC voltage;
• a full-bridge circuit including a first arm composed of a first switching element and a second switching element connected in series with respect to the DC voltage and a second arm composed of a third switching element and a fourth switching element connected in series with respect to the DC voltage;
• a transformer having a single primary coil and an N (N is an integer of 1 or above) number of secondary coils, the primary coil having one end connected to a center point of the first arm, the primary coil having the other end connected to a center point of the second arm;
• an N number of rectifying and smoothing circuits including a rectifying unit connected to each of the secondary coils to rectify an AC voltage generated at the secondary coil, a secondary switching element configured to control an output of the rectified voltage rectified by the rectifying unit, and a smoothing unit configured to smooth the rectified voltage to generate a DC output voltage and supply power to a load;
• an output detecting circuit configured to detect at least one of voltage and current output from the smoothing unit of each of the rectifying and smoothing circuits;
• and
• a control circuit configured to control the first to fourth switching elements and the secondary switching element to turn on/off on the basis of at least one of the detected voltage and the detected current detected by the output detecting circuit,
• wherein the control circuit turns on each of the secondary switching elements during a predetermined time so that the voltage or current output from the smoothing unit of each of the rectifying and smoothing circuits becomes a preset target voltage or target current during a period when the first switching element and the fourth switching element are turn on and during a period when the second switching element and the third switching element turn on.