BJT experts answer please...

Jony130

Joined Feb 17, 2009
5,488
Notice that Q2 base is connected directly to GND and Q1 base to 0.5V. If we assume that Vbe = 0.7V we immediately see that if we assume that Q1 is ON the Ve voltage must by equal to Vb + Veb = 0.5V + 0.7V = 1.2V and this implies that VebQ2 = 1.2V.
But you should know that |Vbe| = 1.2V cannot happen without destroying the transistor. This implies that our assumption (about Q1 is turn on) was wrong. From here we see that Q1 is cut-off (VebQ1 = 0.7V - 0.5V = 0.2V) and Q2 is in active region or in saturation. So, now we can easily find all the voltage in the circuit. Can you do it ?
 

Thread Starter

nPab

Joined Sep 16, 2014
5
Notice that Q2 base is connected directly to GND and Q1 base to 0.5V. If we assume that Vbe = 0.7V we immediately see that if we assume that Q1 is ON the Ve voltage must by equal to Vb + Veb = 0.5V + 0.7V = 1.2V and this implies that VebQ2 = 1.2V.
But you should know that |Vbe| = 1.2V cannot happen without destroying the transistor. This implies that our assumption (about Q1 is turn on) was wrong. From here we see that Q1 is cut-off (VebQ1 = 0.7V - 0.5V = 0.2V) and Q2 is in active region or in saturation. So, now we can easily find all the voltage in the circuit. Can you do it ?
Got it! thanks loads..:D
 

KL7AJ

Joined Nov 4, 2008
2,229
Notice that Q2 base is connected directly to GND and Q1 base to 0.5V. If we assume that Vbe = 0.7V we immediately see that if we assume that Q1 is ON the Ve voltage must by equal to Vb + Veb = 0.5V + 0.7V = 1.2V and this implies that VebQ2 = 1.2V.
But you should know that |Vbe| = 1.2V cannot happen without destroying the transistor. This implies that our assumption (about Q1 is turn on) was wrong. From here we see that Q1 is cut-off (VebQ1 = 0.7V - 0.5V = 0.2V) and Q2 is in active region or in saturation. So, now we can easily find all the voltage in the circuit. Can you do it ?
Just what I was gonna say. :)
 
Top