Abstract: A pre-stage boost device, comprising: a selector switch (130); a power factor inductor (140), a common boost circuit (150), a rectifier circuit (160), and a filter circuit (170). The common boost circuit includes: connected in series a first switch (Q1), a second switch (Q2) and a third switch (Q3). The rectifier circuit includes two rectifier diodes (D5, D6). The filter circuit includes connected in series two capacitors (C1, C2). Maximum multiplexing of the main power components under the battery mode and the commercial power mode is achieved by this invention, the cost to performance ratio is also improved.