10 - 8/22/2005 10: AMPLIFIERS PRELAB FOR FIRST OP-AMP LAB...

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8/22/2005 10: A MPLIFIERS PRELAB FOR FIRST OP-AMP LAB Electrical circuits are CIRCUITS. Every element must have at least two wires and the wiring must eventually come back to the power supply. Circuit diagrams are symbolic pictures of circuits. typical circuit diagram might look like this: S G In general, all branches of the circuit must eventually come back to the negative side of the power source. The negative side of the power supply is often called ground ("G"). Common symbols for circuit diagrams include: Resistor Battery (or power supply) Capacitor Inductor S G Oscillating voltage source Operational Amplifier A In complex circuits, putting in all the ground wires only makes the diagram harder to read. So a new symbol is introduced. Ground
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P108 Lab 10: Page 2 Using this symbol, the example diagram above could be redrawn as follows. S G In general, it is assumed that all the grounds are hooked together. If you want to change the input supply, you can leave it out. In fact, it is usually just assumed that the input voltage is measured with respect to ground, so the simplified diagram becomes: Input Some circuit elements have several inputs and require their own power supply (all of our op-amp circuits, for example). A common op amp circuit is: scope ground +15 V -15 V - + 2 3 6 S G to scope (pins 1, 5, and 8 on the op-amp are not used by us).
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P108 Lab 10: Page 3 All op amps require power, so there is really no need to show it. Using the ground symbol and leaving out the power supplies to the op amp will simplify things considerably. In addition, if we then assume that the input and output are both measured with respect to ground, we get a very simple, easy to read diagram: i nput out put - + Compare this to the first diagram of this circuit. The advantages of the simplified diagram are obvious. However, YOU are responsible for knowing that the op amp requires power and that the input and output devices must be hooked to ground. In fact, the input device, the output device, the power supplies to the op amp, and the + side of the op amp must ALL BE HOOKED TOGETHER, TO A COMMON GROUND. In practice, to build a circuit, it is most important to understand how to unsimplify a schematic diagram. Try it: unsimplify this diagram. i nput out put - +
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P108 Lab 10: Page 4 RESISTOR COLOR CODES Many times we use resistors with particular values to tune the properties of our circuits. The resistor values are often not shown as numbers but instead using a color code consisting of four colored bands. 1st significant figure 2nd significant figure multiplier tolerance Color Code for resistors Significant figures Color Multiplier (Ohm) Tolerance 0 black 1 silver ± 10% 1 brown 10 2 red 100 gold ± 5% 3 orange 1,000 4 yellow 10,000 5 green 100,000 6 blue 1,000,000 7 violet 8 gray 9 white gold 0.1 silver 0.01 For example, a 20 kOhm resistor with 5% tolerance would be red-black-orange-gold (20 x 1000 Ohm ±5%). Try it:
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10 - 8/22/2005 10: AMPLIFIERS PRELAB FOR FIRST OP-AMP LAB...

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