* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ELCE-223 Circuits Lab
Oscilloscope types wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Instrument amplifier wikipedia , lookup
Analog-to-digital converter wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Oscilloscope history wikipedia , lookup
Power MOSFET wikipedia , lookup
Index of electronics articles wikipedia , lookup
Integrating ADC wikipedia , lookup
Surge protector wikipedia , lookup
Flexible electronics wikipedia , lookup
Integrated circuit wikipedia , lookup
Transistor–transistor logic wikipedia , lookup
Power electronics wikipedia , lookup
Audio power wikipedia , lookup
Regenerative circuit wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Wien bridge oscillator wikipedia , lookup
Schmitt trigger wikipedia , lookup
Radio transmitter design wikipedia , lookup
Two-port network wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Negative-feedback amplifier wikipedia , lookup
Current mirror wikipedia , lookup
Rectiverter wikipedia , lookup
Opto-isolator wikipedia , lookup
ENGR-201 Circuits Lab DC Op Amp Circuits Fall 2001 Name:________________________ References: Irwin, Basic Engineering Circuit Analvsis National Semiconductor, Linear Databook, Vol. I Purpose: The goal of this laboratory exercise is to gain hands-on experience with practical operational amplifier (op amp) circuits that have dc input signals. Using dc measurement skills learned earlier, students compare the characteristics of integrated-circuit (IC) op amps with those of the ideal op amp. Background: Because of its versatility and ease of use, the op amp is one of the most widely used electronic devices. Using op amps a designer can easily construct circuits with a wide variety of functions, such as inverting and non-inverting amplifiers, comparators, mixers, regulators, integrators, differentiators, and filters. The op amp is an important electronic device and deserves special consideration by anyone studying electrical engineering. Typical op amp connections are depicted in Figure 1. The device has two input terminals, the inverting (-) and non-inverting (+) inputs, and a single output terminal. Since the op amp is an active device, external power is required to drive internal components. Typically, two power supply connections, V++ and V--are required. All input and output voltages are measured with respect to a single reference (ground); however, there is no reference connection to the op amp itself. Generally, the reference voltage is the common (or ground) of the dc power supplies used to power the circuit, as shown in Figure 1. Figure 1 – Op Amp Connections ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Page: 2 Integrated circuit op amps are available in many different packaging configurations. One popular package is the eight-pin dual in-line package (8-pin DIP). The pin designations for the LM741 and the LF411 op amps packaged in an 8-pin DIP are shown in Figure 2. Only seven of the eight pins are used, and the pin designations are shown in the Table 1. Figure 2 - Pin Definitions of the LM741 and LF411 Op Amp 1 8 2 7 V++ 3 6 + V-- 4 5 Table1 1 - Pin Designations of the LM741 and LF411 Op Amps (8-Pin DIP) Pin # Pin Function 1 Offset Null, used to insure zero output when input is zero 2 Inverting input 3 Non-inverting input 4 V--, the negative power supply connection 5 Offset Null (used in conjunction with pin #I) 6 Output, measured with respect to common 7 V++, the negative power supply connection 8 Not Used (No Connection) The dc power supply connections are sometimes called the bias connections or the positive and negative rails. The output voltage of an op amp circuit is limited by the values of V ++ and V--. In fact, for the typical op amp, the maximum output voltage will be about 1-volt less than the dc supply levels. For example, if the supply voltages are 15V, the output cannot exceed about 14V. When an op amp output reaches the maximum or minimum value established by the dc supply connections, it is said to be saturated. Typical integrated circuit op amps use dc supply voltages in the range 5V to 15V. Some op amps do not require dual (positive and negative) supply values but can work with a single, positive supply. In case a single supply is used, the negative bias pin is generally connected to common. ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Page: 3 The circuit model of the ideal op amp is shown in Figure 3 and consists of three components: an input resistance (Ri), an output resistance (RO), and a voltage-controlled voltage source with gain AVOC (or just AOC). For the ideal op amp, Ri and AOC approach infinity, while RO approaches zero. For the practical op amp, typical values for these parameters fall within the following ranges: Ri: 10M to 106M RO: 10 to 100 AOC: 105 to 106 V/V In order for a practical op amp to behave like an ideal op amp, external resistors used to construct op amp circuits should have values much less than Ri and much larger than RO. Practical op amp circuits, therefore, typically use resistors in the range from a few hundred ohms to a few mega-ohms (M). Using resistors in this range generally will allow a designer to treat the op amp as ideal and provide good approximations for predicting the behavior of the circuit. Figure 3 - Circuit Model of an Op Amp The Inverting Amplifier: An op amp can be used to construct an inverting amplifier by making the connections shown in Figure 4. Select R1 and R2 such that R1 > 47K and R2/Rl 10. The picture attached to the end of this lab shows a typical breadboard construction of an inverting amplifier circuit. Figure 4 – The Inverting Amplifier 10k Figure 4 is a schematic diagram that includes the dc-supply connections; however, this detail is often not provided with an op amp circuit diagram. Remember, an op amp circuit will not work without connecting both dc supplies. For this lab exercise, use V ++ = +12V and V-- = ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Page: 4 -12V. When an op amp (or any circuit) does not work as expected, the dc supply connections are a good place to start looking for the problem. Measure the dc supply voltages at the power supply outputs and at the pins of the op amp. To generate the input voltages specified in Table 2, connect a 10k potentiometer to the dc supply voltages as shown in the diagram. For each input, adjust the potentiometer until the indicated voltage is obtained. Measure the corresponding output and record the value in the table. Compare the measured value of the output voltage with the calculated value and compute the percent difference, D, where D = 100% * (Calculated - Measured) / Calculated Explain any significant differences between the calculated and measured values. measure and record the voltage across the input terminals of the op amp, V id. V1 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 Vid Table 2 - Inverting Amplifier Measurements VO VO % Measured Calculate Difference Comments d Also ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Page: 5 The Non-inverting Amplifier: Figure 5 shows the circuit diagram for a non-inverting amplifier. Note that only two changes need to be made to the inverting amplifier circuit to convert it into a non-inverting amplifier. Remove power from the circuit in Figure 4 and construct the non-inverting amplifier shown in Figure 5 using the same resistor values and dc supply levels. Record the measurements indicated in Table 3 for each input value shown. Explain any significant differences between measured and calculated values. Figure 5 - The Non-inverting Amplifier V++ R1 + Vid 10k - + V2 + VO - - V-- V1 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 Vid Table 3 – Non-inverting Amplifier Measurements VO VO % Measured Calculate Difference Comments d ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Page: 6 The Difference Amplifier: Using the circuit shown in Figure 6, an op amp can be used to generate a signal that is proportional to the difference of two different input signals. This circuit, called a difference amplifier, is useful in instrumentation applications because it tends to cancel out any voltage common to both inputs. Often, this common voltage is "noise", such as interference from ac power lines or radio-frequency (RF) interference. The difference amplifier will reject most of the common-mode noise and amplify the signal of interest. For this reason, most instrumentation amplifiers use a differential (difference) amplifier input stage to minimize signal corruption due to noise. Connect the circuit shown in Figure 6 using the same resistor values for R1 and R2 and in the previous two circuits. Use a 10k-pot and the +5V output of the power supply to set V1 at a constant +0.5V. Use the same voltage divider circuit used with the inverting and noninverting amplifier circuits to vary V2 between -1.0V and +1.0V. Take the measurements indicated in Table 4 and record all measured and calculated values. Explain any significant differences between the measured and calculated values. Va + Vb - + VO - Figure 6 - The Difference Amplifier V2 -1.0 -0.8 -0.4 0 0.4 0.8 1.0 Va Vb VID Table 4 - Difference Amplifier Measurements VO VO % Measured Calculate Difference Comments d ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Page: 7 Questions and Problems 1. Use nodal analysis to derive the voltage gain equations for the inverting, non-inverting, and difference amplifiers. 2. How much resistance does the input signal source see in the inverting amplifier ? In the non-inverting amplifier ? 3. What is the voltage gain of the following amplifier circuit? amplifier makes it particularly useful ? + VIN - What characteristic of this + VO - 4. In a practical op amp circuit, what limits the range of the output voltage? 5. When the output voltage of an op amp reaches its upper or lower limit, what can be said about the voltage across the op amp’s inputs? Examine your measured data (V ID) to answer this question. 6. In the circuit below, determine the power delivered by source V IN and the power delivered to the 100 load. Where is the power supplied to 100 load coming from? + VIN = 25mv - ENGR201 Lab - DC Op Amp Circuits, Fall 2001 Inverting Amplifier Circuit Page: 8