# Is it possible to find Vout in this case ?

1. Dec 3, 2011

### Femme_physics

Last edited by a moderator: May 5, 2017
2. Dec 3, 2011

### technician

FP
I think that diode symbol you have drawn is a zener diode. If so then the Vout is 2V.... that is what zener diodes do.... they set the voltage to what they are designed
It means the voltage across the 1Ω is 4 volts so the current down the series circuit is 4A

3. Dec 3, 2011

### Staff: Mentor

That's a zener diode, so it wants to clamp (limit) the voltage across itself at 2V. So right away you can say that Vout will be in the neighborhood of 2V. This is true so long as the supply voltage is greater than the zener voltage, where the diode starts conducting.

For a more precise figure for Vout you would need to have more information about the particular zener diode's characteristics. They tend to exhibit some resistance that increases with current flow. This one will be drawing about 4 amps!

4. Dec 3, 2011

### Femme_physics

Yes, it's a zener diode.

REally? I didn't know that.

That makes sense! Thanks.

5. Dec 3, 2011

### Femme_physics

Excellent. Yes, we're in basic zener diodes exercises, yet, so I don't think it has any special characteristics.

Thanks a lot gneill, techhie :)

6. Dec 3, 2011

### technician

It's a pleasure
You keep us on our toes
Have probably given too much help.... just realised this is a homework forum

7. Dec 3, 2011

### Staff: Mentor

You're welcome, as always!

If it's early days in zener school , then assume an ideal diode: zero on resistance and a sharp turn-on at its specified voltage.

8. Dec 4, 2011

### Femme_physics

Gotcha.

Actually, this question I asked comes from this question:

http://img35.imageshack.us/img35/8592/myworkp.png [Broken]

I mostly now have a problem figuring out if I should treat the section just above the diode zener (the place I marked "e") as a crossroad, or it should really be a little loop like this:

http://img27.imageshack.us/img27/8527/webcam1322984748.png [Broken]

Last edited by a moderator: May 5, 2017
9. Dec 4, 2011

### technician

This is another weird circuit I would say the diagram should have the loop so that the Zener diode (3V?) is in series with the R above it....but... What is that resistor connected to?
Also I do not understand the 3resistors on the left!
Also.....this is another circuit with no feedback to the - input so the output is certain to be +Vs or -Vs.
It will be interesting to hear the other responses that come your way.

10. Dec 4, 2011

### Femme_physics

I would be very interested, too. And I'd like to know if I can solve it using KCL and KVL only?

11. Dec 4, 2011

### Staff: Mentor

I don't think you'll need even Ohm's law for this one! If that odd loop of resistors between the +12V supply and the + input is correct (no missing ground or power connection) then what determines the voltage on the + input of the op-amp? Hint: What current flows into op-amp inputs?

12. Dec 5, 2011

### Femme_physics

Last edited by a moderator: May 5, 2017
13. Dec 5, 2011

### Staff: Mentor

Actually, not much changes in terms of the result at the output. Can you determine the voltages present on the op-amp inputs?

Last edited by a moderator: May 5, 2017
14. Dec 5, 2011

### technician

Looks "easy" now !!!!!!!!!!

15. Dec 5, 2011

### Femme_physics

Last edited by a moderator: May 5, 2017
16. Dec 5, 2011

### technician

That is what that symbol means. If they were in contact it would (should !!!!!) be shown clearly with a dot on the connection

17. Dec 8, 2011

### Femme_physics

Ah, thanks! So in that case, answering the questions...

A) Find Vout

B) Find Vout when C is shortened to the ground

http://img585.imageshack.us/img585/4126/zelat.jpg [Broken]

Last edited by a moderator: May 5, 2017
18. Dec 8, 2011

### I like Serena

For (A) the plus supply voltage is not -7.5 V.

After that we'll get to (B).

Last edited: Dec 8, 2011
19. Dec 8, 2011

### Femme_physics

What did I do wrong?

20. Dec 8, 2011

### I like Serena

You picked the wrong (the negative) power supply.