Voltage detection/conversion device

The present invention discloses a voltage detection/conversion device composed of: a transfer switch, a full-wave rectifier, a zero-crossing detection circuit, a comparison circuit, and a control unit, wherein one external power source and a backup power supply send the voltage waveform signal to the full-wave rectifier separately to rectify the negative half waveform to the positive half waveform. The phasing waveforms of the two rectified waveforms adjusted by the zero-crossing detection circuit to the same initial timing origin and transmitted to the comparison circuit after the adjustment to compare the amplitude values of the same time. After the control unit received these two amplitudes values and the amplitude of the external power source is less than the amplitude of the backup power source is determined, the switching command will be send to the transfer switch to switch the transfer switch to the backup power source and maintain the machine facilities to operate normally.