Contact potential of Vbe in Q2=Vbe-on
I worked out that the maximum current that can go through R2 is Vbe-on/R2. So my question is why does Q2 turn on when the emitter current of Q1 reaches this maximum current?
Thanks!
Current limit and current gain bjt question
bjtcurrentsemiconductorsvoltage-regulator
Best Answer
What is the voltage across R2?
When the voltage across R2 reaches Vbe-on, what happens with Q2?
Answer those questions and come back with more questions of your own if necessary.
As a side note, it is customary to place a low-value resistor (1k) in series with the base of Q2. This prevents damaging the base of Q2 when a sudden short occurs at the output.