# Homework Help: Compliance Finalization

1. Mar 20, 2014

### Duave

Thank you for any help that you can offer.

1. The problem statement, all variables and given/known data

What is the voltage compliance range of the current source?
Between what range of RL values will the circuit function as a current source?

https://scontent-a.xx.fbcdn.net/hphotos-ash3/t1.0-9/1488711_10151945891295919_440459508_n.jpg

VB = 1.6V
VE = 1.0V
IE = 1.0mA
IL = 1.0mA

2. Relevant equations

VLimit = VCC - ILRE
VCE < V < VLimit

....................................................................... ......
Minimum staturation voltage:

VCE (Sat) = 0.1V
....................................................................... ..................
compliance range is:

VCE < V < VLimit
....................................................................... ..........................................
VCE < V < VCC - ILRE
...............................................
0.1V < V < 10V - 1V
..................................................
0.1V < V < 9V
..................................................

Between what range of RL values will the circuit function as a current source?

The range of load resistors can be found by:

iOUT = Vin/R
.................................................................
VCE/iE < R < (VCC - ILRE)/iL
..................................................................................
0.1V/1.0mA < R < (10V - 1V)/1.0mA
................................................................
100(ohm) < R < 9000(ohm)

Are answers? Are there any errors located?

Last edited: Mar 20, 2014
2. Mar 21, 2014

### Jony130

Can you tell me why you think that for RL<100R this current source won't work?
Also calculate Vce for RL = 9K.

3. Mar 21, 2014

### Duave

So the ranges are incorrect?

4. Mar 21, 2014

### Duave

or correct?

5. Mar 21, 2014

### Jony130

incorrect

6. Mar 21, 2014

### Duave

So the active region is not in between 0.1V and 9V

7. Mar 21, 2014

### Jony130

If you assume that transistor is in saturation region for Vce<0.1V. In this case the active region (Vce range) is indeed between 0.1V and 9V. But still you have incorrect resistor range.

8. Mar 21, 2014

### Duave

Jony130 can you look at what I did and tell me where I went wrong?

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9. Mar 21, 2014

### Jony130

Vce voltage is not the voltage that "appears" across RL resistor.
V_RL = Vcc - Vce - Ve. So for Vce = 0.1V --->V_RL = (10V - 0.1V - 1V) = 8.9V.
And if Vce = 9V --->V_RL = ??

10. Mar 21, 2014

### Duave

I'm lost .

I knew my answers were incorrect.

V(limit) was said to be the maximum before saturation

so the compliance voltage range is okay.

the load resistance range is not

so what do I do? Cause I don't get this now

11. Mar 21, 2014

### Jony130

Do you see the difference between Vce voltage and voltage across RL resistor?

12. Mar 21, 2014

### Duave

Vce is a junction voltage, The voltage across RL is a branch voltage,

But I don't understand this range business.

What does range mean with respect to Vce and RL?

13. Mar 21, 2014

### Jony130

Q1. What is the voltage across V_RL if Vce = 0.1V ?
Q2. What is the voltage across V_RL if Vce = 9V ?

14. Mar 21, 2014

### Duave

See I confused because I wasn't given an RL value,

Ic = Ie only during the active region so I have no currents,

I'm stuck like a duck.

15. Mar 21, 2014

### Jony130

You don't need to know RL value. First we need to know V_RL voltage range. Next we can use this range to find RL value. The only think you need is to find V_RL range by using KVL and find V_RL voltage.

16. Mar 21, 2014

### Duave

Vcc-(ILxRL) - Vce = 0

10V-(IL x RL) -0.1 = 0

9.9V -(ILxRL) = 0

9.9V = ILxRL

9.9V/IL = RL

9.9V/1.0mA = RL

9.9 k(ohm) = RL

17. Mar 21, 2014

### Jony130

18. Mar 21, 2014

### Duave

Vcc-(ILxRL) - Vce -Ve = 0

10V-(IL x RL) -0.1 - 1V= 0

8.9V -(ILxRL) = 0

8.9V = ILxRL

8.9V/IL = RL

8.9V/1.0mA = RL

8.9 k(ohm) = RL

So is this the lower or the upper limit?

19. Mar 21, 2014

### Jony130

Finally, some good work.
What do you think ?