Voltage compliance and load resistor range for BJT current source

[Duave]

Thank you for any help that you can offer.

Did I answer the questions?

Homework Statement

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

V_B = 1.6V
V_E = 1.0V
I_E = 1.0mA
I_L = 1.0mA

Homework Equations

VLimit = VCC - I_LR_E
V_CE < V < V_Limit

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

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

V_CE < V < V_Limit
............. .........
VCE < V < VCC - I_LR_E
.........
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:

i_OUT = V_in/R
............
V_CE/i_E < R < (VCC - I_LR_E)/i_L
...............
0.1V/1.0mA < R < (10V - 1V)/1.0mA
............
100(ohm) < R < 9000(ohm)
Are answers? Are there any errors located?

Thanks again for your help.

 

[Jony130]

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

 

[Duave]

So the ranges are incorrect?

 

[Duave]

or correct?

 

[Jony130]

incorrect

 

[Duave]

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

 

[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.

 

[Duave]

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

 

[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 = ??

 

[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

 

[Jony130]

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

 

[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?

 

[Jony130]

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

 

[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.

 

[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.

 

[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

 

[Jony130]

You forget about Ve voltage.

 

[Duave]

You forget about Ve voltage.

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?

 

[Jony130]

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

Finally, some good work.

So is this the lower or the upper limit?

What do you think ?