1. a.k.a.: Draw in the Diamond
Engineering 43
OpAmp Tutorial
a.k.a.: Draw in the Diamond
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
Engineering-43: Engineering Circuit Analysis
Bruce Mayer, PE 1
• ENGR-43_OpAmp_Tutoria.ppt

2. Picture: Sp11 MTE1 OpAmp Problem

3. Sp11 MTE1 OpAmp Errors Calc of v+ as +/− 41V
Assumes voltage across 5 mA current source is ZERO!!!
V+ Actually 6V
Failure to Recognize that OpAmp can Source or Drain current
i.e., assumed that IOA = 0
Shoud be IOA = mA
Assuming that the Voltage across the 3 mA source is ZERO!!!
NO Calc, at all, of v+
Just Assumed v− = 0
Failure to use Virtual Short  v+ = v−
Using GND Node for KCL withOUT considering the OpAmp GND
Relates to IOA = 0 error

4. Suggestions to Improve
SHOW on OpAmp Symbol Dependent Voltage Diamond
as source of “infinite” output current
Connection to GND to emphasize KCL for OpAmp OutPut Current
On Example Find Power-Conditions for Isrc’s  find Voltage relative to GND Between
3m Source and 0.5k Resistor
5m Source and 8k Resistor

5. Picture
Even though VOLTAGE across Diamond is FORCED to ALMOST-ZERO by FeedBack, the Diamond CURRENT is NOT ZERO. Indeed, the Diamond SETS the Current so that it’s Voltage is Vo/Ao. In this example Vo is 5V+9V = 14V. If Ao = , the V+ − V− = 14V/ = 112 μV = mV