LED backlight driver module design circuit

Circuit analysis: The requirement of the backlight driver is that the brightness of the backlight LED remains unchanged under any conditions, that is, a constant current source circuit needs to be constructed. The backlight drive circuit shown in the figure is the simplest constant current source circuit. When the circuit is working, the voltage across resistor R9 is equal to VLL1 plus the BE conduction voltage, which is a fixed voltage of about 1.7V. The current flowing through R9 is also fixed. The current is approximately equal to the emitter current and collector current of Q2, so the current flowing through the backlight diode D1 is also a constant current, realizing the constant current drive of the backlight LED. The driving current of the backlight LED is about 10mA, and the value of R9 is 150Ω.