When the expected driving current of LED strings LED1, LED2, and LED3 is determined, the reference current signal can be regulated by the PWM control signal to match the expected driving current. The state of power switching transistor Q can be controlled in accordance with current feedback signal VFB and the reference current signal by multichannel constant current LED controlling circuit U1 to control the output current of the power stage circuit to be consistent with the expected driving current of LED strings LED1, LED2, and LED3. The luminance of LED strings LED1, LED2, and LED3 may also be different for warm-and-cold lamp applications. Therefore, the duty cycle of the PWM dimming signals can be correspondingly regulated in accordance with the luminance requirement. In addition, an average current of each LED string can be regulated to achieve corresponding luminance by controlling the operation of switching transistors Q1, Q2, and Q3 in accordance with the PWM dimming signals by multichannel constant current LED controlling circuit U1.