Reference signal generator and PWM control circuit for LCD backlight

A PWM control circuit for LCD backlight, comprising:

• a variable resistance unit configured to provide a variable resistance that changes sequentially in accordance with a load control signal acquired by a logical OR operation of an initial driving completion signal and a protection signal for soft frequency changing;
• a current control unit configured to control a current flowing through the variable resistance unit and a current flowing through a current generating unit in accordance with the variable resistance provided by the variable resistance unit;
• the current generating unit configured to generate a variable current that sequentially changes, based on a control of the current control unit;
• a reference signal generating unit configured to control charging of a voltage until a charged voltage charged by the variable current generated by the current generating unit reaches a first reference voltage level, to start discharging of the charged voltage when the charged voltage reaches the first reference voltage level, to control the discharging until the charged voltage reaches a second reference voltage level, and to generate a triangular wave reference signal having a predetermined frequency buffering interval in which a frequency changes sequentially when the initial driving completion signal or the protection signal is input;
• and
• a PWM control unit comprising an inverted input terminal configured to receive the reference signal from the reference signal generating unit as an input and two non-inverted input terminals configured to receive an error amplifier voltage and a soft start voltage, the PWM control unit outputting a pulse-width modulated signal by comparing the reference signal, the error amplifier voltage, and the soft start voltage, wherein
• when the load control signal is the initial driving completion signal of a low level, the variable resistance unit is configured to provide the variable resistance for the soft frequency changing in which a frequency is decreased from a high initial driving frequency to a low normal driving frequency,
• when the load control signal is the protection signal of a high level, the variable resistance unit is configured to provide the variable resistance for the soft frequency changing in which the frequency is increased from the low normal driving frequency to a high protection driving frequency, and
• the variable resistance unit comprises:
• a first resistor having a first end and a second end, the first end being connected to a first power source voltage terminal;
• a first diode having a cathode and an anode, the cathode being connected to the second end of the first resistor;
• a second resistor having a first end and a second end, the first end being connected to the anode of the first diode;
• a third resistor connected between the second end of the second resistor and a ground;
• a fourth resistor having a first end and a second end, the first end being connected to a first connection node between the first resistor and the first diode;
• a first capacitor connected between the second end of the fourth resistor and the ground;
• and
• a voltage variable switch connected to the first capacitor in parallel, and configured to be turned on when the load control signal is the high level and turned off when the load control signal is the low level.