1. Electronic Troubleshooting Chapter 8 Operational Amplifiers

2. Operation Amplifiers Overview Original OP-Amps 1940/50’s Tube circuits Discrete component semi-conductor circuits followed I the first monolithic ICs started appearing in the 1960s The first was in 1963 The 741 was released in 1968 Packaging Cans DIPs Surface mount Picture from Wikipedia, see the terms of use on their site.

3. Operation Amplifiers Overview Characteristics Multistage amplifier Coupling Cap Simplified drawing on the top Complementary Symmetry output » Low output impedance Some have FETs on the input Bottom - simplified drawing of LF351 » 741 replacement

4. Op Amp Basic configuration Open Loop Gain Ideal Gain = infinity Actual = 200k into millions Input Impedance Ideal = infinity Real mega ohms Output impedance Ideal = zero Actual ranges to less than 1 ohm

5. Inverting Amplifier See formulas on the bottom of page 192 and example on 193 Critical to understanding operation with feedback

6. Noninverting Amplifier See formulas on the middle of page 193 and example on 194

7. Voltage Follower

8. Amplify AC Signals

9. Open Loop Voltage Gain vs Freq 741

10. Finding Upper Cut-off Frequency

11. Compensate Op Amp Some very old OP-Amp ICs require external components to prevent high freq oscillations, such as Fairchild’s 709 Data Sheet: http://www.datasheetcatalog.com/datasheets_pdf/L/M/7/0/LM709.shtmlhttp://www.datasheetcatalog.com/datasheets_pdf/L/M/7/0/LM709.shtml

12. Voltage Follower in AC Circuit

13. Differential Amplifiers Characteristics Uses ICs instead of discrete components Gain is based R F and R 1 RA and RB also factor into the operation Use 10 and 100K and walk through

14. Differential Amplifiers Characteristics Only the difference between signals should be amplified How well this is accomplished in an actual Op-Amp is measured by the Common Mode Rejection Ratio - CMRR Ideally – infinite Actual is listed in the manufacturers specification sheet Common Mode Gain Example Problem 8-5 on page 198

15. Integrator

16. Level Detector Characteristics As shown the circuit is a zero crossing detector Swap the inputs and its an inverting zero crossing detector Detecting other levels besides zero volts Back to original drawing: add a DC voltage to the inverting input You now have a level detector for that voltage Swap the inputs and you have an inverting detector

17. Level Detector Zero Crossing Non-Inverting Zero Crossing Inverting

18. Level Detector Positive Voltage Level Detector Non-Inverting Positive Voltage Level Detector Inverting

19. Level Detector Negative Voltage Level Detector Non-Inverting Negative Voltage Level Detector Inverting

20. Level Detector w/Noise Tolerance Level Detector Non-Inverting w/Positive feedback

21. Level Detector w/Noise Tolerance Level Detector Non-Inverting w/Positive feedback Formulas V UT = V Ref (1+1/n) - (-V sat /n) V LT = V Ref (1+1/n) - (+V sat /n) V Ctr = (V UT - V LT )/2 = V Ref (1+1/n) V H = V UT - V LT = {(+V sat ) - (-V sat )}/n

22. Level Detector w/Noise Tolerance Level Detector Inverting w/Positive feedback

23. Level Detector w/Noise Tolerance Level Detector Inverting w/Positive feedback Formulas V UT = V Ref (n/{n+1}) + (+V sat /{n+1}) V LT = V Ref (n/{n+1}) + (-V sat /{n+1}) V ctr = (V UT + V LT )/2 = V Ref (n/{n+1}) V H = V UT - V LT = = {(+V sat ) - (-V sat )/(n+1)}

24. LM339 Comparator

25. Comparator Squaring Circuit

26. Lo-Battery Indicator Op-Amp is configured as a 1.5V level detector

27. Locating Faults IC failures Almost always from Handling Misuse Typical misuse/Handling problems Power supply voltages that are too high – Check datasheets Power supply connections are reversed Simple protection is possible » Use some diodes

28. Locating Faults IC failures Typical misuse/Handling problems Too large of input voltages If max input is below 0.7V » Use diodes » Else use zener diodes

29. Locating Faults IC failures Typical misuse/Handling problems Output shorted Small resister sized to prevent the max output current from being exceeded See page 206

30. Other problems FET problems Zero Problems See page 206 for discussion