107_19b - 1 Electrical Engineering Technology EET 107...

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Unformatted text preview: 1 Electrical Engineering Technology EET 107 Introduction to Circuit Analysis Lecture # 19.b Professor Robert Herrick Purdue University © EET 107 - 19 Introduction to Circuit Analysis 2 Inverting Positive Feedback Comparator Closed Loop Purdue University © EET 107 - 19 Introduction to Circuit Analysis 3 Inverting, Positive Feedback Rf positive feedback Feedback loop +Esupply Ri Vout Verror Vin inverting Inverting comparator Input ! Purdue University © Rail Voltage −Esupply EET 107 - 19 Introduction to Circuit Analysis 4 Inverting, Positive Feedback − Rf Feedback loop +Esupply − positive feedback Ri − − − Verror Vin inverting comparator Purdue University © + −Esupply EET 107 - 19 Vout Rail Voltage Same sign. Positive feedback ! Introduction to Circuit Analysis 5 Positive Feedback Rf positive feedback Ri Feedback loop +E supply Rail Voltage Vout Vin inverting comparator −Esupply Positive feedback adds to Verror Verror é Vout é Verror é etc. Slams UPPER or LOWER rail ! UPPER LOWER Purdue University © EET 107 - 19 Introduction to Circuit Analysis 6 Inverting è Two Possible Vout Rf positive feedback Feedback loop +Esupply Ri Vout Verror Vin inverting comparator Rail Voltage SLAMS RAIL ! −Esupply Vout = UPPER RAIL Verror > 0 V Vout = LOWER RAIL Verror < 0 V Purdue University © EET 107 - 19 Introduction to Circuit Analysis 7 Inverting Positive FB – LOWER RAIL + VRf − Rf I 0V + VRi − Ri 1k +3 V Vin a0 A + Verror − 9k Iin op amp = 0 A I +12 V Vout −12 V − 10 V rail Feedback current I through Rf & Ri Essentially series circuit with current I ! Purdue University © EET 107 - 19 Introduction to Circuit Analysis 8 Positive Feedback – UPPER RAIL + VRf − Rf I 0V + VRi − a Ri 1k +3 V Vin 9k I +12 V + Vout Verror − −10 V rail −12 V Draw the series circuit without the op amp. Find I, VRI, Va, and V error. Purdue University © EET 107 - 19 Introduction to Circuit Analysis 9 Inverting Positive FB – LOWER RAIL VRi = 1mA • 1kΩ = 1V 1V + VRf − Rf I 0V + VRi − a Ri 1k +3 V Vin 9k I +12 V + Verror − −10 V rail Vout −12 V Va = 0V − 1V = −1V Verror = −1V − (+3V) = −4V Vout è LOWER RAIL Enet = 0V – (10V) = 10V RT = 1kΩ + 9kΩ = 10kΩ Vout = − 10 V Ι = 10V / 10kΩ = 1 mΑ Purdue University © EET 107 - 19 ü Slams lower rail Introduction to Circuit Analysis 10 Positive Feedback – UPPER RAIL −VRf + Rf 9 k I 0V − VRi + −3 V +12 V a + Ri 1k Vin I Vout Verror − +10 V rail −12 V Draw the series circuit without the op amp. Find I, VRI, Va, and V error. Purdue University © EET 107 - 19 Introduction to Circuit Analysis 11 Inverting Positive FB – POSITIVE RAIL VRi = 1mA • 1kΩ = 1V 1V −VRf + Rf 9 k I 0V − VRi + a Ri 1k −3 V Vin I +12 V + +10 V rail Vout Verror − −12 V Va = 0V + 1V = +1V 1V Verror = +1V − (−3V) = 4V Vout è UPPER RAIL Enet = 10V – (0V) = 10V RT = 1kΩ + 9kΩ = 10kΩ Vout = + 10 V Ι = 10V / 10kΩ = 1 mΑ Purdue University © EET 107 - 19 ü Slams upper rail Introduction to Circuit Analysis 12 Trip Point Sweep Vin from +3V to −3V What is the trip point? Purdue University © EET 107 - 19 Introduction to Circuit Analysis 13 TRIPS at Verror = 0V VRT = 0V−(−10V) = 10V 10 + VRf − Rf 9k I 0V + VRi − a Ri 1k Vin I I = 10V / 10kΩ = 1mA +12 V + 0V − Vout −10 V rail −12 V Sweep from +3V to –3V Vri = 1mA • 1kΩ = 1V Va = 0V − (1V) = −1V Vin = −1V − 0V= −1V Trips at Verror = 0V Purdue University © Trips at V in= −1V EET 107 - 19 Introduction to Circuit Analysis 14 Transfer Curve: Vin sweep + to − Circuit trips from Vout −10V to +10V rail +10 V at Vin −1V Verror = 0V Vin = −1V −10 V Purdue University © EET 107 - 19 Introduction to Circuit Analysis 15 Sweep Vin from –3V to +3V What is the trip point? Purdue University © EET 107 - 19 Introduction to Circuit Analysis 16 TRIPS at Verror = 0V VRT = 10V − (0V) = 10V 10 −VRf + Rf 9 k I 0V − VRi + +12 V a Ri 1k Vin I + 0V − Vout +10 V rail −12 V I = 10V / 10kΩ = 1mA Vri = 1mA • 1kΩ = 1V Va = 0V + 1V = +1V Sweep from −3V to +3V Vin = +1V + 0V= +1V Trips at Verror = 0V Purdue University © Trips at V in= +1V EET 107 - 19 Introduction to Circuit Analysis 17 Transfer Curve: Vin sweep − to + Circuit trips from Vout +10V to −10V rail +10 V at 1V Vin Vin = +1V −10 V Purdue University © Verror = 0V EET 107 - 19 Introduction to Circuit Analysis 18 Full Transfer Curve for Inverting Positive Feedback Comparator Purdue University © EET 107 - 19 Introduction to Circuit Analysis 19 Inverting, Positive FB Vout +10 V upper trip point UTP −1V LTP lower trip point 1V Vin −10 V Hysterisis Loop Purdue University © EET 107 - 19 Introduction to Circuit Analysis 20 Inverting Positive Feedback Comparator Closed Loop Purdue University © EET 107 - 19 Introduction to Circuit Analysis ...
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This note was uploaded on 02/22/2012 for the course ECET 107 taught by Professor Staff during the Fall '08 term at Purdue University-West Lafayette.

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