Effects of Load on Diode Circuit with Exponential Model

[vermin]

Homework Statement

The circuit in the diagram utilizes three identical diodes
having I_S = 10−16 A. Find the value of the current I required
to obtain an output voltage V_o = 2.4 V.

If a current of 1 mA is drawn away from the output terminal by a load, what is
the change in output voltage?

Homework Equations

What does the value of I_S tell me? should I multiply that by the # of diodes, 3(10^(-16)) A, plug that into the 'exponential equation' I have in my notes and solve for 'i'?

Really not sure what's going on here. Going back to read the text again.

The Attempt at a Solution

What I tried is using i=I_S(e^(V_D/V_T)-1)
using 25 mV for V_T, and 0.8 V for V_D (2.4/3). Got that, 7.9 mA for i, the current required. Yay.

The next part I don't know what they mean. What would a 1 mA current drawn away do to the output voltage? How do you express that?

In general I'm finding myself doing plug and chug and kind of flying blind with someone else's equations. A big picture description of what I'm trying to figure out, for starters.

 

[gneill]

The Attempt at a Solution

What I tried is using i=I_S(e^(V_D/V_T)-1)
using 25 mV for V_T, and 0.8 V for V_D (2.4/3). Got that, 7.9 mA for i, the current required. Yay.

The next part I don't know what they mean. What would a 1 mA current drawn away do to the output voltage? How do you express that?

In general I'm finding myself doing plug and chug and kind of flying blind with someone else's equations. A big picture description of what I'm trying to figure out, for starters.

A load connected at the terminal V_o that "steals" 1 mA will reduce the current through the diodes accordingly, hence changing the diode potential drops. That's just KCL applied at the junction of the current source and diode chain.