A linear dimming LED driver circuit capable of adjusting color temperature used in a lamp of a down light or a tube light to drive a plurality of LED strings to emit light and the LED strings are formed by yellow-light and ultra blue LEDs. The circuit uses a switch to switch the conduction of the LED strings to change the color temperature of the light emission of the lamp, so that the control module will adjust the light emitting brightness of the lamp for better dimming range and work performance of the whole circuit if a driving voltage is in a mono sinusoidal voltage section greater than or equal to 129 volts and smaller than or equal to 135 volts.