107_20a - 1 Electrical Engineering Technology EET 107...

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Unformatted text preview: 1 Electrical Engineering Technology EET 107 Introduction to Circuit Analysis Lecture # 20.a Professor Robert Herrick Purdue University © EET 107 - 20 Introduction to Circuit Analysis 2 Summary Noninverting Negative Feedback Amplifier Purdue University © EET 107 - 20 Introduction to Circuit Analysis 3 Nonverting, Negative Feedback noninverting amplifier +Esupply Vin + Verror − negative feedback A Vout −Esupply Rf f Ri Purdue University © EET 107 - 20 Introduction to Circuit Analysis 4 Nonverting, Negative Feedback + noninverting amplifier + Vin + + Verror − negative feedback Noninverting +Esupply A + Vout −Esupply Rf f Ri Purdue University © EET 107 - 20 Introduction to Circuit Analysis 5 Nonverting, Negative Feedback + noninverting amplifier + Vin +Esupply A Verror − negative feedback + −Esupply + f Rf + Ri Purdue University © Negative FB + − + Vout + Signal & FB signal opposite signs Signal gets smaller ! EET 107 - 20 Introduction to Circuit Analysis 6 Negative Feedback Negative feedback subtracts from V error Verror ê Vout ê Verror ê etc. Verror Verror Verror Verror Purdue University © EET 107 - 20 Approaches 0V Introduction to Circuit Analysis 7 Negative Feedback As long as Vout op amp not saturated (not at a rail) Verror ≅ 0V Amplifier with controlled voltage gain Purdue University © EET 107 - 20 Introduction to Circuit Analysis 8 Negative Feedback Verror Vout Op Amp not at RAILS ! < A Verror 10 V < < 100 µV ≈ 0 V 5 10 Purdue University © EET 107 - 20 Introduction to Circuit Analysis 9 Negative Feedback Amplifier Iin op amp = 0 A Verror = 0 V Feedback current If through Rf & Ri Essentially series circuit with current I ! Purdue University © EET 107 - 20 Introduction to Circuit Analysis 10 Voltage Follower - Simplest 1V +15 V Vin + 0V − 1V Output follows input. Same voltage & sign as input ! 1V A = 105 Vout −15 V f Noninverting Negative Feedback Iin op amp = 0A Verror = 0V Purdue University © 1V Vf = 1V – 0V = 1V Vout = Vf = 1V 1V Verror = ? EET 107 - 20 Introduction to Circuit Analysis 11 Voltage Follower - Simplest 1V +15 V Vin + 0V − 1V 5 A = 10 Vout Verror = ? −15 V f Verror 1V < 5 < 10 µV ≈ 0 V 10 Purdue University © EET 107 - 20 J Introduction to Circuit Analysis 12 Noninverting, Negative Feedback Amplifier 0A 100 mV Vin 0A +15 V Iout op amp + 0V − A=10 5 −15 V 100 mV Vout Rf 3.3 k f Ri If If 1k Purdue University © EET 107 - 20 Introduction to Circuit Analysis 13 Noninverting, Negative Feedback Amplifier 0A 100 mV Vin 0A +15 V Vf = 100mV – 0V = 100mV Iout op amp + 0V − A=105 VRi = 100mV – 0V = 100mV −15 V 100 mV Vout Rf 3.3 k f Ri 1k If If 430 mV If = 100mV/1kΩ = 100µA VRf = 100µA × 3.3kΩ = 330mV Vout = 100mV + 330mV = 430mV 430mV Unloaded ! Purdue University © EET 107 - 20 Introduction to Circuit Analysis 14 Noninverting, Negative Feedback Amplifier 0A 100 mV Vin 0A A=105 f −15 V Vout Rf 3.3 k If Ri − 330mV + 1k 100mV − Iout op amp + 0V − 100µA 100 mV + +15 V If 430 mV 100µA Purdue University © EET 107 - 20 Introduction to Circuit Analysis 15 Noninverting, Negative Feedback Amplifier 0A 100 mV Vin 0A +15 V Iout op amp + 0V − A=105 −15 V Vout Rf 3.3 k f Ri If 1k If Rload 10 Iload + Vload − LOAD Effect Purdue University © EET 107 - 20 Introduction to Circuit Analysis 16 Noninverting, Negative Feedback Amplifier 0A 100 mV Vin 0A +15 V Great amplifier but there is a but Iout op amp + 0V − A=10 5 −15 V Vout Rf 3.3 k f Ri 1k If If Rload 10 Iload + Vload − problem with this load current ! ! ! this Vload = Vout = 430mV Iload = 430mV / 10Ω = 43 mA 43 Too much op amp current! What to do? Purdue University © Iop amp out = 43mA + 0.1mA = 43.1mA 43.1mA EET 107 - 20 Introduction to Circuit Analysis 17 BJT Current Booster +15 V 100 mV IE = If + Iload=43.1mA +15 V Iout op amp Vin A=105 0.86 mΑ 43 mΑ Rf 3.3 k Ri 1k IB ≅43mA/50=0.86mA IE −15 V f Silicon β = 50 If Rload 10 Iload + Vload − Iout op amp= 0.86mA J Cool Op Amp ! Purdue University © EET 107 - 20 Introduction to Circuit Analysis 18 Summary Noninverting Negative Feedback Amplifier Purdue University © EET 107 - 20 Introduction to Circuit Analysis ...
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