# Op-amp questions

Discussion in 'Homework Help' started by Digit0001, Jun 1, 2012.

1. ### Digit0001 Thread Starter Member

Mar 28, 2010
89
0
Hi

View attachment op_amp_qns.pdf

I have the two question where i cannot seen to get the right answers

Can someone help me with question 1 part c),d)

in part b) i get Vp=1/(20*2pi) = 0.00795 what have i done wrong?

Also in question 2 i cannot get the answer of 10mA

This is what i get: performing a KVL i get 0.7+Ie*R1-12-2.7=Ie=Iz=14/.200=70mA

what have i done wrong in this question?

P.S

Last edited: Jun 1, 2012
2. ### WBahn Moderator

Mar 31, 2012
18,093
4,920
I've only got time right now to help with Question #2.

When you say the answer is supposed to be 10mA, is that for Io or for Iz?

The equation you give makes no sense. First off, the units don't work out.

0.7+Ie*R1-12-2.7 These are all voltages.

0.7+Ie*R1-12-2.7=Ie And now it is equal to a current?

0.7+Ie*R1-12-2.7=Ie=Iz And why is the emitter current equal to the zener current?

Q1) What assumption can you make about the base current? Why?
Q2) What is the voltage at the base of the transistor?
Q3) What is the voltage across R2?
Q4) What is the current through R2?
Q5) What is the current through the zener diode, Iz?
Q7) What is the voltage at the emitter of the transistor?
Q8) What is the voltage across R1?
Q9) What is the current through R1?
Q10) What is the collector current?

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
In Q1 part b

Presumably you are using

Vout[max]=10Vp=(Slew Rate)/ω

Vp=(Slew Rate)/(10ω)=10^6/(10*2*∏*20*10^3)=0.796 Volts

You just need to work in consistent units.

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
For Q1 part c

Using the previous method - what would you estimate as the useful frequency range? Then compare that frequency with the bandwidth based on the anticipated [design] gain and transition frequency. The lower of the two values would be your logical answer.

5. ### Digit0001 Thread Starter Member

Mar 28, 2010
89
0
thanks for the reply after going through it again i worked it out. The Iz is not equal to Io so the answer should be different.