Chapter 25: Electronics
Exercise 25.3 Inverting and non-inverting amplifiers This exercise helps develop your understanding of op-amps when used in more complicated circuits, in particular to make use of feedback and gain. 1 An operational amplifier (op-amp) uses negative feedback in practical amplifier circuits. a State what is meant by negative feedback. b State two effects on the operation of the amplifier of using negative feedback. 2 This circuit shows an inverting amplifier: 60 kΩ
20 kΩ
P
+9 V − +
0.10 V
−9 V
Vout
The open loop voltage gain of the amplifier is very high. a State what is meant by the open loop voltage gain. b Explain why a high gain means that P can be taken as almost at earth potential (0 V). c Calculate the current in the 20 kΩ input resistor. d Explain why the currents in the 20 kΩ input resistor and the 60 kΩ resistor are equal. e Calculate Vout. f
Calculate the gain of the amplifier.
g State the effective input resistance of the amplifier. h Describe what happens to Vout if the input voltage 0.10 V is removed and, instead, a voltage is applied that changes from −2 V to +2 V. i
State the value of Vout if the input voltage is +6 V.
3 This circuit shows a non-inverting amplifier: +9 V P
− +
Vin
−9 V
R Vout 10 kΩ
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