A driving circuit is provided, which is configured to supply a driving voltage and a driving current to an LED string. A first detection resistor is arranged on a path of the LED string. A voltage source outputs a control voltage having a level that corresponds to the target luminance level of the LED string, and a first threshold voltage that is proportional to the control voltage. A controller generates a gate pulse signal having a duty ratio that is adjusted such that the voltage drop across the first detection resistor matches the control voltage. A first driver drives a switching transistor of a DC/DC converter according to the gate pulse signal. When the voltage drop across the first detection resistor exceeds the first threshold voltage, a first comparator stops the switching operation of the switching transistor.