Q1 AND Q2 form a pair of transistors , when current through Q1 increases, R12 and R13 will sample a larger voltage and then the
base voltage of Q2 will decrease and current through Q2 increases , this will decrease the current through Q1 , so it can stabilize the
current through Q1. VERY SIMPLE[br]<p align=right><font color=red>+3 RD币</font></p>