Chapter 3 problems

3.9

Part A

• Using KVL: $4=1.5I_A+V_A$
• Thus the two points for the load line are $V_A=4$ and $I_A=2.66$
• Overlay the above two points with the diode characteristics to find the answer.

Part B

• Is there a physical part that mimics the device characteristics of X?
• Using KCL: $-.005+V_b/200+I_b=0$
• Thus: $I_b=.005$ and $V_b=1$, however this is off the chart. Is this correct?

Part C

• Using KCL: $-V_C/500+I_C+V_C/500=0$
• I believe there is a problem with my equation.

3.17

Part A

• Guessing D1 is on, D2 and D3 are off. Looking at the voltage drops, this is very unlikely.
• Guessing D1 off, D2 on, D3 off. $I=7.5mA$ and $V=7.5$.

• Checking for positive current through presumed on diodes and negative voltage across the presumed off diodes.
• D1 and D2 fail. D3 passes.

• Guessing D1 and D2 on, D3 off.

• $I=0$ and $V=7.5$. D1, D2, D3 pass.

Check each guess please. More importantly, check the wrong assumptions.

Part B Need help on this one.

• $V_{in}=0$, $V=-5$: D1, D4 on. D2, D3 off.
• $V_{in}=2$, $V=-5$: D1, D4 on. D2, D3 off.
• $V_{in}=6$, $V=5$: D2, D3 on. D1, D4 off.
• $V_{in}=10$, $V=5$: D2, D3 on. D1, D4 off.

V=0. D1, D4 on. Can you really sink current into a voltage source? I don't see how you will ever have negative voltage across the diodes.