Patent ID: 8139019

Claim:
A brightness adjusting device comprising: a multiplication circuit multiplying an input dimming synchronization signal with a multiplication ratio to output a multiplication signal; a detection circuit connected to the multiplication circuit, the detection circuit to detect an operation start edge of the multiplication signal and to generate an output signal based on the detected operation start edge; a sawtooth wave generator connected to the detection circuit to generate a sawtooth wave having constant amplitude independently of the multiplication signal based on the output signal; a first reference voltage generator that generates a first reference voltage; and a comparator connected to the sawtooth wave generator to output a pulse signal by comparing a voltage of the sawtooth wave with the first reference voltage, wherein the first reference voltage generator comprises a circuit that outputs a variable voltage, and the multiplication circuit comprises a circuit having a variable multiplication ratio, wherein the detection circuit comprises: a first resistor having a first end receiving an input signal; a condenser having a first end connected to a second end of the first resistor; a diode having an anode connected to a ground and a cathode connected to a second end of the condenser; and a second resistor having a first end connected with the cathode of the diode and the second end of the condenser, and a second end connected to the ground.