who can explain how the following circuit works?

[SparkZhang]

I am confused with the bellow circuit which is used to drive a LCD backlight. who can help me to explain it briefly,thank you very much in advance~!

 

[jony130]

Q2 and Q3 it's a on/off transistor.
When Q3 is open Q2 is open to, so the Vbat is applied to the boost converter .
And L1, Q1, D5 and PWM driver work as a boost converter.

 

[SparkZhang]

thank you very much for your information. could you tell how the Vout be converted to 18V maybe while the Vbat is only about 4V?

 

[jony130]

Well we can achieve this thanks to L1 and his Inductance. Being more precise thanks to L1 self-inductance.
If you interesting in details please read this:
Understanding the Inductor on 22 page.
https://www.elsevierdirect.com/samplechapters/9780750679701/9780750679701.PDF
https://en.wikipedia.org/wiki/Boost_converter#Overview

 

[SparkZhang]

thank you very much, jony~! it's very useful information you have provided.