Patent ID: 7541695

Claim:
An uninterruptible power supply connected to a commercial power supply and a load having a capacitive element, comprising: a controller; a first switch circuit connected to the commercial power supply and the controller; a second switch circuit connected to the controller and one end of the load for performing a switching operation in response to the driving of the controller; a transformer having a first winding, a second winding, and a third winding, wherein the first winding is connected to the other end of the load and the first switch circuit and the second switch circuit, and wherein the second winding is connected to the second switch circuit; a charging circuit connected to the third winding; an energy accumulation device connected to the charging circuit; a DC-DC converter connected to the energy accumulation device for boosting a DC voltage outputted from the energy accumulation device; and an inverter connected to the first winding and the DC-DC converter for converting a boosted DC voltage outputted from the DC-DC converter into a first AC voltage and delivering the first AC voltage to the load; wherein when the energy accumulation device is supplying power, the controller manipulates the first switch circuit to turn off and a second AC voltage is induced in the second winding in response to the first AC voltage which is delivered to the first winding, such that the second AC voltage regulates a voltage level of the first AC voltage according to a connection status between the second switch circuit and the second winding.