A light-emitting diode driving system including a load, a power supply circuit and a light-emitting diode driving device is provided. The load includes one or more light-emitting diode strings. The power supply circuit outputs an output voltage to drive the load according to a feedback signal. The light-emitting diode driving device includes at least one current source, at least one comparator and a control logic circuit. The current source outputs a current to drive the load. The comparator compares a first voltage from the current source to a reference voltage and outputs a second voltage according to a comparison result. The control logic circuit includes a control node. The control logic circuit receives the second voltage through the control node and converts the second voltage to a control signal to adjust a resistance value of a variable resistor circuit. A light-emitting diode driving device is also provided.