A driver circuit for driving an LED array is disclosed. The LED array includes a first, a second, a third, a fourth LED device and a diode device. The second LED device is connected to the first LED device. The fourth LED device is connected to the third LED device. The diode device is connected between the second LED device and the third LED device. The driver circuit includes a first constant current regulator for coupling between the first and the second LED device; a second constant current regulator for coupling between the second and the third LED device; a third constant current regulator for coupling between the third and the fourth LED device; a fourth constant current regulator for coupling between the fourth LED device and a fixed-voltage terminal; and a control circuit coupled with the first, the second, the third, and the fourth constant current regulators.