The invention relates to a DC-DC converter having over-current/over-voltage protection function and an LED driving circuit using the same. The DC-DC converter adjusts a width of a switching pulse outputted from a Pulse Width Modulation (PWM) controller to control on/off durations of a switch, thereby providing a controlled level of voltage to a load. The DC-DC converter includes a microcontroller for detecting a voltage, and if the detected voltage is greater than a reference voltage, generating an alarm signal. The DC-DC converter further includes a digital-analogue converter for outputting a voltage of 0V and an analogue dimmer for generating a control signal that changes an `on` duration of the switching pulse outputted from the PWM controller to 0 and providing the control signal to the PWM controller.