The invention relates to a PWM (
Pulse Width Modulation) light adjusting technology for an LED (
Light Emitting Diode) and aims at providing a circuit for realizing the
voltage-self-
adaptation PWM light adjustment of the LED under the drive of a prepositive constant-
current source. The circuit comprises an output load LED string LED1, an output
filter capacitor Co1, a forestage controlled direct-current (DC) source Is1 and a PWM light adjusting
control circuit which is connected with the LED string LED1, wherein the
filter capacitor Co1 is in parallel connection with the two terminals of the controlled
DC source Is1, the LED string LED1 is in series connection with the PWM light adjusting
control circuit and then in parallel connection with the two terminals of the Is1, and a light adjusting
signal input terminal is connected to the control terminal of the controlled
DC source Is1. According to the circuit for realizing the
voltage-self-
adaptation PWM light adjustment of the LED under the drive of the prepositive constant-
current source, the forestage constant-
current source and the rear-stage PWM
control circuit are out of additional
signal circuit connection, besides being in power connection, so that the control is simple; the average terminal of the rear-stage PWM pulse
constant current source obtains the minimum
voltage through
self adaptation, so that the conduction losses are reduced; the PWM light adjustment of the LED can be realized without PWM light adjusting signals; the M light adjusting function is realized in an analog mode, so that the cost is low; and the multichannel PWM light adjusting control can be realized by adopting a multichannel output
constant current source, and only light adjusting signals of one channel are used.