lab5_u11_Op_Amps - University of Florida Department of...

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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Ode Ojowu, TA Page 1/6 Revision 0 17-Jun-11 Lab 5: Operation Amplifiers Figure 1 – Three-terminal op amp symbol. Figure 2 – A741 op amp symbol Figure 3 –741 op amp symbol in Multisim 741 3 2 4 7 6 5 1 OBJECTIVES To verify the operational amplifier theory and analysis. To successfully interpret and implement a chip pin-out diagram. To reinforce and verify typical operational amplifier circuit configurations. MATERIALS The lab assignment (this document) Your lab parts. LM741 datasheet (on our website) Pre-lab questions including Multisim Printouts (required) of the below documents: o Pre-lab analyses o Multisim screenshots e-mailed to course e-mail Graph paper INTRODUCTION Op Amp Brief Description Operational amplifiers (op amps) are important components of many electronic circuits. Although internally an op amp is an extremely sophisticated electronic circuit, the external operation can be understood without reference to the internal components. In other words, an op amp can usually be considered to be a “black box” component. The simplified op amp circuit diagram symbol is shown in Fig. 1. The negative-designated terminal is called the inverting input terminal , the positive-designated terminal is called the non-inverting input terminal , and terminal on the right is the output terminal . Inputs of positive and negative DC supply voltages are required, but they are often not shown on the circuit diagram. Fig. 2 shows a uA741 Operational Amplifier circuit and includes both the power supply pins (labeled V+ and V-). The two offset null voltage inputs (labeled OS1 and OS2) are rarely used and we will not discuss them. Fig. 3 shows a 741 op amp symbol in Multisim. Ideal Op Amp Model The input terminals usually terminate on an insulating material. Consequently, the input currents are so small that they can usually be neglected and can be considered to be zero. It is important to remember this important approximation of zero input currents . Do not think that because the input currents can be considered to be zero that the current in the output line is zero. The output current is seldom zero. Thus, KCL does not apply to a closed surface around the op amp symbol of Fig. 1. There is also an important approximation for the voltage across the input terminals. If the output voltage is less in magnitude than the supply voltages, which it is for normal (non-saturated) operation, the voltage across the input terminals is so small that it can be considered to be zero . This approximation of zero volts across the input terminals is extremely important to remember in the
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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Ode Ojowu, TA Page 2/6 Revision 0 17-Jun-11 Lab 5: Operation Amplifiers determination of op amp circuit operation. Although there is approximately zero volts across the input
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lab5_u11_Op_Amps - University of Florida Department of...

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