Direct-current residual-current detecting device

A direct-current residual-current detecting device, driven by a monopolar power supply, comprises: a power conversion self-balancing circuit (102), a residual-current transformer (106), and a comparator (108). An input end of the power conversion self-balancing circuit (102) is connected to the monopolar power supply, the power conversion self-balancing circuit (102) converts monopolar power into bipolar power and outputs the bipolar power, and the power conversion self-balancing circuit (102) supplies power to another component. The residual-current transformer (106) is provided with an RL multivibrator, a square wave pulse voltage drive circuit (104) circularly exerts positive and negative direction voltages to a secondary winding of the residual-current transformer (106), and the residual-current transformer (106) outputs a corresponding sampling voltage. The comparator (108) obtains the sampling voltage output by the residual-current transformer (106), compares the sampling voltage with a voltage threshold of the comparator, and generates a positive and negative alternately square wave signal, the square signal is fed back as output of the comparator (108) to the square wave pulse voltage drive circuit (104) as a drive signal, and output of the comparator (108) is further used as output of the direct-current residual-current detecting device to represent the polarity and size of a direct-current residual-current.