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 number of secondary coils, where N is an integer of 1 or above, the primary coil having one end connected to a node between the first switching element and the second switching element of the first arm, the primary coil having the other end connected to a node between the third switching element and the fourth switching element of the second arm;
• an N number of rectifying and smoothing circuits, each rectifying and smoothing circuit comprising:
• a rectifying and switching unit connected to each of the secondary coils to rectify an AC voltage generated at the secondary coil and to control an output of a rectified voltage, the rectifying and switching unit having one terminal connected to one of the secondary coils and another terminal connected to a secondary ground, 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 rectifying and switching unit 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 rectifying and switching elements in each of the rectifying and switching units such that, in each duty cycle of the respective rectifying and switching units, the control circuit turns on at least one rectifying and switching element at a first predetermined time after turning on the first switching element and the fourth switching element, and the control circuit turns off the at least one rectifying and switching element at a second predetermined time prior to turning off each of the first switching element and the fourth switching element,
• the control circuit turns on the at least one rectifying and switching element such that, in each duty cycle of the respective rectifying and switching units, the control circuit turns on at least another of the rectifying and switching elements at a third predetermined time after turning on the second switching element and the third switching element, and the control circuit turns off the at least another rectifying and switching element at a fourth predetermined time prior to turning off the second switching element and the third switching element, and
• the control circuit turns on each of the rectifying and switching units so that, in each duty cycle of the rectifying and switching units, 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 turn on and during a period when the second switching element and the third switching element turn on,
• wherein each of the rectifying and switching units includes a first MOS-type FET having a drain connected to one end of each of the secondary coils, and a second MOS-type FET having a drain connected to the other end of each of the secondary coils,
• wherein a source terminal of the first MOS-type FET and a source terminal of the second MOS-type FET are connected to the secondary ground,
• wherein a gate terminal of the first MOS-type FET and a gate terminal of the second MOS-type FET are respectively connected to the control circuit, and
• wherein the first MOS-type FET and the second MOS-type FET rectify an AC voltage generated at the secondary coil.