The invention includes two parallel paths. A first path is composed of two contact ends of a first electronic switch and a first, third and fifth diodes, which connect in series. One contact end connects a first end of an AC source, and a control end connects a second end of the AC source. A second path is composed of two contact ends of a second electronic switch and a second, fourth and sixth diodes, which connect in series. One contact end connects the second end of the AC source, and a control end connects the first end of the AC source. The AC source is connected between the positive ends of the first and second diodes. The second end of the AC source separately connects negative ends of the first and third diodes through two capacitors. The first end of the AC source separately connects negative ends of the second and fourth diodes through another two capacitors. Negative ends of the fifth and sixth diodes connect together to form a voltage output end.