Patent ID: 8829859

Claim:
A device for charging batteries at least comprising a controllable sinusoidal wave power, a small-signal voltage detecting circuit, and a phase comparator; wherein, said controllable sinusoidal wave power receiving an output phase contrast signal of said phase comparator for changing an output frequency of said sinusoidal wave power until said output phase contrast signal of said phase comparator equals to zero or a determined value; said small-signal voltage detecting circuit measuring a charging voltage of said batteries and filtering out a DC part thereof for attaining a small-signal voltage signal, so that said small-signal voltage signal is simultaneously amplified and transmitted to said phase comparator; and said phase comparator receiving a current phase signal from said controllable sinusoidal wave power and a voltage phase signal from said small-signal voltage detecting circuit for comparing a phase contrast therebetween and transmitting a comparing result to said controllable sinusoidal wave power.