Patent ID: 7230353

Claim:
A charging circuit in a back-up power system, comprising: an output terminal electrically connected to a main power for providing an AC output voltage; a transformer having a secondary electrically connected to said output terminal; an electrical energy storage and supply device providing a DC current; an inverter having an output electrically connected to a primary of said transformer and an input electrically connected to said electrical energy storage and supply device and comprising four gate control switch devices to form a bridge switching device, wherein said four gate control switch devices respectively have an anti-parallel diode; a first diode having an anode electrically connected to one output terminal of said bridge switching device; a second diode having an anode electrically connected to the other output terminal of said bridge switch device; and a charging switch device having a first conducting terminal electrically connected to a common cathode of said first and said second diodes and a second conducting terminal electrically connected to a negative electrode of said electrical energy storage and supply device so as to charge said electrical energy storage and supply device through a conduction state and a cut-off state of said charging switch device.