Patent ID: 8760076

Claim:
A pulse width modulation (PWM) dimming circuit, comprising a switch unit, a current generation unit, a mirror current source, a multi-path output unit, a plurality of current balance units and a plurality of LED lamp strings, wherein the switch unit is configured to receive a PWM signal and is controlled to turn on or off by the PWM signal; the current generation unit is connected with the switch unit and is configured to generate a current of a predetermined magnitude when the switch unit is turned on; the mirror current source is connected with the current generation unit and is configured to receive the current generated by the current generation unit and to generate a mirror current; the multi-path output unit is connected with the mirror current source and is configured to receive the mirror current and output the mirror current in multiple paths; the number of the current balance units is equal to that of the LED lamp strings, and the plurality of current balance units are connected between the multi-path output unit and the plurality of LED lamp strings respectively and are configured to adjust respective resistances to keep balance of currents among the LED lamp strings; the current generation unit comprises a resistor (RSET), an operational amplifier (OP 1 ) and a metal oxide semiconductor (MOS) transistor (Q 1 ); the resistor (RSET) has one end thereof connected to the switch unit and the other end thereof connected to an inverting input terminal of the operational amplifier (OP 1 ) and a source of the MOS transistor (Q 1 ); the operational amplifier (OP 1 ) has a positive input terminal connected to a first reference voltage and an output terminal connected to a gate of the MOS transistor (Q 1 ); and the MOS transistor (Q 1 ) has a drain connected to the mirror current source.