Abstract: A DC-DC converter includes a voltage input module receiving an input voltage from an exterior power supply, a voltage transforming module connected with the voltage input module for transforming the input voltage into a proper output voltage, a voltage output module connected with the voltage transforming module for supplying the proper output voltage to an exterior electric appliance, a first detecting module connected with the voltage output module for detecting an output current of the voltage output module and sending a corresponding current signal, a second detecting module connected with the voltage output module for detecting the output voltage of the voltage output module and sending a corresponding voltage signal, and a control module for receiving and analyzing the corresponding current and voltage signals and then generating a corresponding control signal so as to control the output voltage of the voltage transforming module for protecting the electric appliance.