107_19a - 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.a Professor Robert Herrick Purdue University © EET 107 - 19 Introduction to Circuit Analysis 2 Summary Temperature Sensor Comparator Positive Feedback Comparator Purdue University © EET 107 - 19 Introduction to Circuit Analysis 3 Temperature Sensor Comparator Open Loop Purdue University © EET 107 - 19 Introduction to Circuit Analysis 4 Temperature Sensor Comparator +5V °T +5V LM 34 Vin + 10mV/°F Verror LM324 − Vref Vout op amp 10 k Rpot bottom Purdue University © EET 107 - 19 R2 100 +5V Green R1 −5V 10 k Red 150 Introduction to Circuit Analysis 5 Temperature Sensor Comparator +5V °T Vin + 10mV/°F Verror − Vref 10 k +5V series LM324 RAILS +5V LM 34 10 k LM324 0Α −5V Vout op amp Red series Green series R2 100 Rpot bottom R1 +3.5V -4.2V 150 1.28kΩ Referrence to freezing 32° F Purdue University © Vref EET 107 - 19 1.28 kΩ = (5 V ) = 320 mV 20 kΩ Introduction to Circuit Analysis 6 Temperature Sensor Comparator +5V Temperature Signal °T +5V LM 34 Vin + 10mV/°F Verror − Vref Vout op amp −5V 10 k +5V 10 k 1.28kΩ 320mV Rpot bottom Purdue University © Red Green R1 R2 100 150 32° F EET 107 - 19 Introduction to Circuit Analysis 7 Temperature Sensor at 20°F 20 °F +5V Vin = 20 °F (10mV/ °F) = 200mV °T 20 °F 200 mV LM 34 +5V Vin −4.2 V + 10mV/°F Verror V− −4.2 V Vout op amp ref −5V 10 k +5V 10 k 32 °F 320 mV Rpot bottom Red R1 100 − 2V + − 2.2 V + Verror= 200mV−320mV = −120mV Green R2 150 Verror < 0 Vout op amp = lower rail Op Amp limited Purdue University © Vout op amp = −4.2V IGREEN = 2.2V/150Ω=14.7mA EET 107 - 19 Introduction to Circuit Analysis 8 Temperature Sensor at 35°F 35 °F °T +5V LM 34 35 °F 350 mV +5V Vin 3.5 V + Verror − Vref 10mV/°F 10 k +5V 10 k Vin = 35 °F (10mV/ °F) = 350mV V out op amp − 5V 32 °F 320 mV Rpot bottom 3.5 V + 2V − + 1.5 V − Red Green R1 R2 100 150 Verror=350mV−320mV= 30mV Verror > 0 Vout op amp = upper rail Careful! Op amp current limited. Purdue University © Vout op amp = 3.5V 3.5 IRED = 1.5V/100Ω=15mA EET 107 - 19 Introduction to Circuit Analysis 9 Op Amp Comparator • Jitter around reference ! • Voltage Gain A = 100,000 • Op amp extremely sensitive to very low noise ! • Not good if controlling heavy duty compressor ! Purdue University © EET 107 - 19 Introduction to Circuit Analysis 10 Noninverting Positive Feedback Comparator Closed Loop Purdue University © EET 107 - 19 Introduction to Circuit Analysis 11 Noninverting, Positive Feedback positive feedback Feedback loop Rf +Esupply Vin Ri noninverting comparator Purdue University © Vout Rail Voltage −Esupply EET 107 - 19 Introduction to Circuit Analysis 12 Positive Feedback positive feedback Vin +R i + + ++ noninverting comparator Feedback loop Rf +Esupply + + Vout Rail Voltage −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 13 Only Two Possible Vout positive feedback Feedback loop Rf +Esupply Vin Ri noninverting comparator Vout 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 14 Positive Feedback – UPPER RAIL positive feedback I +3 V Vin − VRf + Rf 10 k − VRi + Ri 1k noninverting comparator a Iin op amp = 0 A I +12 V + Vout Verror − −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 15 Positive Feedback – UPPER RAIL positive feedback I +3 V Vin − VRf + Rf 10 k − VRi + Ri 1k noninverting comparator a 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 16 Positive Feedback – UPPER RAIL positive feedback I +3 V Vin Rf 10 k − VRi + Ri 1k noninverting comparator VRi = 0.636mA•1kΩ = 0.636V 0.636V − VRf + a I Va = 3V+0.636V = 3.636V +12 V + Verror − +10 V rail Vout −12 V Verror = Va−Vcom = 3.636V Vout è UPPER RAIL Enet = 10V – (3V) = 7V RT = 1kΩ + 10kΩ = 11kΩ Vout = +10 V +10 Ι = 7V / 11kΩ = 0.636 mΑ 0.636 Purdue University © EET 107 - 19 ü Slams upper rail Introduction to Circuit Analysis 17 Positive Feedback – LOWER RAIL + VRf − Rf 10 k I −3 V Vin + VRi − Ri 1k a 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 18 Positive Feedback – LOWER RAIL VRi = 0.636mA•1kΩ = 0.636V 0.636V + VRf − Rf 10 k I −3 V Vin + VRi − Ri 1k a I +12 V + Vout Verror − −10 V rail −12 V Va = −3V−0.636V = −3.636V Verror = Va −Vcom = − 3.636V Vout è LOWER RAIL Enet = −3V – (−10V) = 7V RT = 1kΩ + 10kΩ = 11kΩ Vout = −10 V Ι = 7V / 11kΩ = 0.636 mΑ 0.636 Purdue University © EET 107 - 19 ü Slams lower rail Introduction to Circuit Analysis 19 TRIPS to Other Rail at Verror = 0V − VRf + Rf 10 k I − VRi + Vin Ri 1k a I +12 V + 0V − Vout +10 V rail −12 V Sweep V in from +3V to –3V. What V in is requird to trip to –10V lower rail at Verror = 0V ? Purdue University © EET 107 - 19 Introduction to Circuit Analysis 20 TRIPS at Verror = 0V − VRf + Rf 10 k I − VRi + Vin Ri 1k a Va = 0V I +12 V + 0V − Vout +10 V rail −12 V VRf = 10V−0V = 10V 10 10 IRf = 10V / 10kΩ = 1mA Vri = 1mA • 1kΩ = 1V Sweep from +3V to –3V Vin = 0V − 1V = −1V 0V Trips at V in= −1V Trips at Verror = 0V Purdue University © EET 107 - 19 Introduction to Circuit Analysis 21 Transfer Curve: Vin sweep + to − Circuit trips from Vout +10V to –10V rail +10 V at −1V Vin Verror = 0V Vin = −1V −10 V Purdue University © EET 107 - 19 Introduction to Circuit Analysis 22 Sweep Vin from –3V to +3V What is the trip point? Purdue University © EET 107 - 19 Introduction to Circuit Analysis 23 TRIPS at Verror = 0V + V Rf − Rf 10 k I + VRi − Vin Ri 1k a Va = 0V I +12 V + 0V − Vout −10 V rail −12 V Sweep from −3V to +3V VRf = 0V − (−10V) = 10V 10 IRf = 10V / 10kΩ = 1mA Vri = 1mA • 1kΩ = 1V Vin = 0V + 1V= +1V 0V Trips at Verror = 0V Purdue University © Trips at V in= +1V EET 107 - 19 Introduction to Circuit Analysis 24 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 25 Full Transfer Curve for Noninverting Positive Feedback Comparator Purdue University © EET 107 - 19 Introduction to Circuit Analysis 26 Noninverting, Positive FB Vout lower trip point +10 V LTP −1V 1V Vin UTP upper trip point −10 V Hysterisis Loop Purdue University © EET 107 - 19 Introduction to Circuit Analysis 27 Temperature Sensor Comparator Positive Feedback Comparator 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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