A detecting circuit includes an indicating light, a switch component, and a control component. The indicating light indicates whether a voltage rail output by a power supply is within a predetermined voltage range. The switch component has a first terminal connected to the voltage rail, a second terminal connected to the indicating light, and a control terminal. The control component is connected to the control terminal of the switch component. The control component switches on the switch component to power on the indicating light when the voltage rail is within the predetermined voltage range, or switches off the switch component to power off the indicating light when the voltage rail is out of the predetermined voltage range.