Patent ID: 6917125

Claim:
An uninterruptible switching power supply device, comprising: a main transformer ( 200 ) having a primary winding ( 201 ) and a secondary winding ( 202 ); a high voltage switching circuit ( 10 ) comprising a DC high voltage bus ( 108 ), a high voltage switch ( 109 ), and an AC input power being coupled to the primary winding ( 201 ) through a rectifying circuit ( 103 ) and said DC high voltage bus ( 108 ); at least one low voltage switching circuit ( 20 ) comprising a battery ( 400 ), a low voltage switch ( 402 ) being coupled to the positive pole of the battery ( 400 ) through a diode ( 401 ), and a tap L from the secondary winding ( 202 ) of the main transformer ( 200 ); and a pulse width modulator unit ( 302 ) for controlling the high voltage switching circuit ( 10 ) and the low voltage switching circuit ( 20 ) to operate synchronically; wherein number of turns NL from said tap L to the reference ground is determined by the following equation: NL=V Bmax N H /V Hmin wherein V Bmax is the maximum discharging voltage of the battery ( 400 ) at the tap L, V Hmin is the minimum AC voltage when the battery begins to discharge, and N H is the number of turns of the primary winding ( 201 ) of the main transformer ( 200 ).