What is the Voltage Compliance Range of a Current Source?

[Duave]

Thank you for any help that you can offer.

Did I answer all of the questions correctly and thoroughly? Can you please find any errors, and point them out to me so that I can fix them?

Homework Statement

Show that :

V_B = 1.6V
V_E = 1.0V
I_E = 1.0 mA
I_L = 1.0 mA
What is the voltage compliance range of the current source?
For what range of load resistors R_L will the circuit function as a current source?

https://scontent-a.xx.fbcdn.net/hphotos-prn1/t1.0-9/1012267_10151937081750919_819156677_n.jpg

Homework Equations

R_B1/R_B2 = {10V - V_B}/V_B
...................
I_L = I_E = V_B - 0.6/R_E
.................
V_Limit < V_comp < {V_RE/R_E}R_L = 1.03mA[/B]
.....................
i_out = V_in/R_E
............

The Attempt at a Solution

2(a)₁

R_B1/R_B2 = {10V - V_B}/V_B
..................
8.2k/1.6k = {10V - V_B}/V_B
.............
5.125V_B = {10V - V_B}
............
5.125V_B + V_B = 10V
............
6.125V_B = 10V
........
V_B = 10V/6.125
.......
V_B = 1.63V
......

2(a)₂
.......
I_L = I_E = V_B - 0.6/R_E
.................
I_L = I_E = 1.63 - 0.6/1000k
.............
I_L = I_E = 1.03/1000k
............
I_L = I_E = 1.03mA
..........
V_B - V_BE = V_E
.............
V_E = 1.03V
......
V_E/R_E = 1.03V/1000k
............
I_E = V_E/R_E = 1.03mA
...............


What is the voltage compliance range of the current source?

The device is in comlpliance when:

V_Limit < V_comp < {V_RE/R_E}R_L = 1.03mA[/B]
...............
V_CC - I_LR_E < V_comp < {V_RE/R_E}{V_CC/I_E}
.................
10V - (0.001A)(1000[ohms]) < V_comp < {1V/1000[ohms]}{10V/0.001A}
.....................
10V - 1V < V_comp < 10V
.........
9V < V_comp < 10V
.........


For what range of load resistors R_L will the circuit function as a current source?

The range of load resistors can be found by:

i_out = V_in/R_E
............
9V/1000[ohms] < V_comp/R_L[ohms] < 10V/1000[ohms]
...................
Your assistance will be greatly appreciated

 

[rude man]

"Compliance range" needs to be better defined.

The circuit is a current source for R_L only if the 8.2K resistor stays at +10V.
Then you can determine how low Vcc to R_L can be before the transistor saturates.

There is in addition a high voltage limit due to the breakdown voltages of the transistor, but that can't be determined with the data you're given.

The last question's answer depends on the voltage to R_L as well as the value of R_L, so I guess assume Vcc = 10V for R_L.

 

[Duave]

"Compliance range" needs to be better defined.

The circuit is a current source for R_L only if the 8.2K resistor stays at +10V.
Then you can determine how low Vcc to R_L can be before the transistor saturates.

There is in addition a high voltage limit due to the breakdown voltages of the transistor, but that can't be determined with the data you're given.

The last question's answer depends on the voltage to R_L as well as the value of R_L, so I guess assume Vcc = 10V for R_L.

@rude man


Thank you. I will make corrections.

 

[Duave]

@rude man,


If the compliance voltage is the range of output voltage in a constant current (dc) power supply over which the load regulation is within certain limits, how can I use this knowledge to verify that my last answer is correct. Can the variable load resistor range from 0 to 8k4 ohms. If it is higher than that, what will happen?

Thank you

 

[rude man]

If your load is 8000 ohms, what is the collector voltage going to be?
If it's 9000 ohms, what then?

Hint: if the emitter to collector voltage is < about 0.2V the transistor is in saturation.

BTW this is not voltage compliance. It assumes the voltage to RL is a constant +10V.

Voltage compliance is a function of R_L. Try to figure out how low the voltage at the top of R_L can be for a given R_L.