Switching power supply and display device provided the same
A switching power supply has a function of improving a power factor, and outputs insulated DC. The switching power supply performs two kinds of controls for switching devices exclusive to each other: controlling of a switching device provided in a direction in which the discharging of a primary-side smoothing capacitor is prohibited at the time of suspension of commercially available AC power and near the zero cross of an input voltage; and causing a switching device provided between the output side of a third winding and the primary-side smoothing capacitor to control a charging current, thereby charging a capacitor in a boosted manner.
1. A switching power supply into which AC power is input and which outputs DC power electrically insulated from the AC power, the switching power supply comprising:
a first rectification-smoothing unit that rectifies and smooths the AC power;
an insulation transformer that includes at least a primary winding, a secondary winding, and a third winding;
a second rectification-smoothing unit which is connected to the secondary winding, rectifies and smooths AC power from the secondary winding and outputs DC power;
a first switching device that is connected between a DC-side terminal of the first rectification-smoothing unit and the primary winding;
an inrush current suppressing unit which is connected to the primary winding in parallel therewith and which includes a second switching device;
a charge storing unit that is connected to a DC side of the first rectification-smoothing unit;
a third switching device that is connected in series to the DC side of the first rectification-smoothing unit so as to prevent the charge storing unit from discharging;
a charging circuit that charges the charge storing unit with power from the third winding in a boosted manner;
a fourth switching device which is connected between the charging circuit and the charge storing unit and which controls a charging current of the charging circuit;
a power factor improving control unit which controls the first, second, third and fourth switching devices and which improves a power factor of the AC power to be input; and
a power-suspension detecting unit that detects a power suspension of the AC power,
the third switching device being controlled when the power-suspension detecting unit detects a power suspension of the AC power in order to cause the charge storing unit that stores a charge in advance to discharge the insulated DC power to an output side through the insulation transformer.
2. The switching power supply according to claim 1 , wherein the charging circuit includes:
a diode connected to an input side from the third winding;
a capacitor connected to the diode and the third winding in parallel with the diode and the third winding; and
a coil connected to a charging path from the capacitor to the charge storing unit.
3. The switching power supply according to claim 2 , wherein
when the power-suspension detecting unit determines that an input voltage of the commercially available AC power is high, the third switching device is controlled so as to halt an operation thereof, and the fourth switching device is controlled so as to charge the charge storing unit until a hold voltage thereof becomes a predetermined set value, and
when the power-suspension detecting unit determines that the input voltage of the commercially available AC power is low, the fourth switching device is controlled so as to halt an operation thereof, and the third switching device is controlled in order to cause the charge storing unit storing a charge in advance to discharge, thereby discharging and outputting the insulated DC power to an output side through the insulation transformer and the second rectification-smoothing unit.
4. A display unit comprising the switching device according to claim 3 as a power converting device.
5. A display device comprising the switching device according to claim 2 as a power converting device.
6. The switching power supply according to claim 1 , wherein
when the power-suspension detecting unit determines that an input voltage of the commercially available AC power is high, the third switching device is controlled so as to halt an operation thereof, and the fourth switching device is controlled so as to charge the charge storing unit until a hold voltage thereof becomes a predetermined set value, and
when the power-suspension detecting unit determines that the input voltage of the commercially available AC power is low, the fourth switching device is controlled so as to halt an operation thereof, and the third switching device is controlled in order to cause the charge storing unit storing a charge in advance to discharge, thereby discharging and outputting the insulated DC power to an output side through the insulation transformer and the second rectification-smoothing unit.
7. A display device comprising the switching device according to claim 6 as a power converting device.
8. A display device comprising the switching device according to claim 1 as a power converting device.