SOFT START CONTROL CIRCUIT HAVING TWO FUNCTIONS

摘要

PURPOSE: A soft start control circuit having two functions is provided to control an initial soft start process of an inverter circuit and a PWM(Pulse Width Modulation) dimming process by using one pin and one capacitor. CONSTITUTION: A startup circuit(100) is used for determining an initial state of an RS latch(200) and initializing an operation of an inverter. The RS latch(200) has a reset terminal(R) for receiving an output signal of the startup circuit(100), a set terminal(S) for receiving an output signal of the first comparator(COMP1), and an output terminal for operating a switch(400). A soft start pin(300) is used for increasing a signal input to control brightness of a backlight. The first capacitor(C1) is used for charging or discharging the first current source(I1). The first comparator(COMP1) outputs a comparative voltage the set terminal(S) of the RS latch(200). The second comparator(COMP2) outputs a triangular wave to an inversion terminal. The switch(400) is used for charging current source to the first capacitor(C1). A transistor(Q23) performs a switching operation.