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Anglicky v odborných předmětech "Support of teaching technical subjects in English “

Anglicky v odborných předmětech "Support of teaching technical subjects in English “. Tutorial : Mechanic – electrician Topic : Electronics II. class Operational Amplifiers : Non- Inverting Amplifiers – Part 2 – Derivations Prepared by: Ing. Jaroslav Bernkopf.

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Anglicky v odborných předmětech "Support of teaching technical subjects in English “

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  1. Anglicky v odborných předmětech"Support ofteachingtechnicalsubjects in English“ Tutorial: Mechanic– electrician Topic: Electronics II. class OperationalAmplifiers: Non-InvertingAmplifiers – Part 2 – Derivations Prepared by: Ing. Jaroslav Bernkopf Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002 je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

  2. Voltage Gain Let‘s apply a voltage V1 of +1 V to the input of the amplifier in the figure. Thevoltagedifferencebetweentheinputs V+ and V- iszero. Thisimpliesthatthevoltage on the input V- isthesame as the input voltage, i.e. +1 V. This voltage will cause a current to flow through the resistor R1. What will this current be? V+ V1 = +1 V V- +1 V Operational Amplifiers

  3. Voltage Gain The voltage across the resistor R1 is 1 V. Using the Ohm‘s law we can calculate the current through the resistor R1: V+ V1 = +1 V V- +1 V VR1 = 1 V IR1 = 1 mA Operational Amplifiers

  4. Voltage Gain • Can thiscurrentflow fromthe input V-? • No, it can‘t, because as we know • the input resistance of an op amp is infinite • the input current of an op amp is zero • So the current ofthe resistor R1 has to flowthroughR2. V+ V1 = +1 V V- IR2 = 1 mA +1 V VR1 = 1 V IR1 = 1 mA Operational Amplifiers

  5. Voltage Gain The current of 1 mA will create a voltage drop across the resistor R2. We can calculate it using the Ohm‘s law: VR2 = IR2 * R2 VR2 = 1mA * 10k VR2 = 10 V V+ V1 = +1 V VR2 = 10 V V- IR2 = 1 mA +1 V VR1 = 1 V IR1 = 1 mA Operational Amplifiers

  6. Voltage Gain What is the value and thepolarity of the output voltage? Theupper end of R1 is positive withrespect to theground. We can draw a small plus sign to theupperendof R1, a minus sign to itslowerend. Thecurrentthrough R2 isthesame as thecurrentthrough R1: Itflowsfromabove to below. Wecandrawthesame plus and minus signs to theendsof R2. V+ V1 = +1 V + VR2 = 10 V V- IR2 = 1 mA - +1 V + VR1 = 1 V - IR1 = 1 mA Operational Amplifiers

  7. Voltage Gain The output voltageconsistsof the sum of twoindividual resistor voltage drops. These voltage drops are in series, liketwobatteries. Theirvoltagesaddtogether. Thetotal output voltage V2 is V2 = VR1 +VR2 V2 = 1 V + 10 V V2 = 11 V The output voltageis positive and itsvalueis +11 V. V+ V1 = +1 V + VR2 = 10 V V- IR2 = 1 mA - +1 V V2 = +11 V + VR1 = 1 V - IR1 = 1 mA Operational Amplifiers

  8. Voltage Gain • What is the voltage gain? • As youcan see, the amplifier makes • elevenvolts out of one volt • positive output voltage out of positive input voltage • Its voltage gain must be +11. V+ V1 = +1 V + VR2 = 10 V V- IR2 = 1 mA - +1 V V2 = +11 V + VR1 = 1 V - IR1 = 1 mA Operational Amplifiers

  9. Voltage Gain Look at the voltages and at the values of the resistors: Do the values look so similar just by accident? No, it is no accident. V+ V1 = +1 V + VR2 = 10 V V- IR2 = 1 mA - +1 V V2 = +11 V + VR1 = 1 V - IR1 = 1 mA Operational Amplifiers

  10. Voltage Gain The voltage gain is determined by the voltages: The voltages are determined by the values of the resistors. Therefore, the voltage gain is determined by the resistors: V+ V1 = +1 V + VR2 = 10 V V- IR2 = 1 mA - +1 V V2 = +11 V + VR1 = 1 V - IR1 = 1 mA Operational Amplifiers

  11. Voltage Gain This is the equation we are looking for: Now you can forget it. Because in future you will always be able to derive it again. V+ V1 = +1 V + VR2 = 10 V V- IR2 = 1 mA - +1 V V2 = +11 V + VR1 = 1 V - IR1 = 1 mA Operational Amplifiers

  12. Task • Construct the first stage of a preamplifier for record players. • The preamplifier should have the following features: • Input resistance Rin = 47kΩ • Voltage gain Av = 34 • Use the conception shown in the figure below. V+ V- Operational Amplifiers

  13. Solution The input resistance Rinof anon-inverting amplifier is infinite. Thedesired input resistanceRinof thepreamplifieris 47 kΩ. Ri = ∞ V+ V- Rin = ∞ Operational Amplifiers

  14. Solution Wemustaddanotherresistor R3 = 47k in parallel to achievethe desired input resistance Rin= 47kΩ. V+ V- Rin = 47k Operational Amplifiers

  15. Solution Thevaluesof R1 and R2 are not given. Let‘schoosetheresistanceof R1 = 1kΩ. Thenwewillcalculatethevalueof R2. V+ V- 1k Operational Amplifiers

  16. Solution The equationforthevoltage gain is: 1 Let‘s express R2: Let‘s substitute theknownvaluesforAv and R1: V+ 33k 1k V- Rin = 47k Theresistanceof R2 willbe33 kΩ. 1k Operational Amplifiers

  17. References • http://www.wikipedia.com • http://www.thefreedictionary.com Operational Amplifiers

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