Introduction to Electronics
Introduction to Electronics PH 245
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This 2 page Class Notes was uploaded by Giovanna Yost on Tuesday September 22, 2015. The Class Notes belongs to PH 245 at Colorado State University taught by Staff in Fall. Since its upload, it has received 47 views. For similar materials see /class/210315/ph-245-colorado-state-university in Physics 2 at Colorado State University.
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Date Created: 09/22/15
Prof John Harton Office D203 Physics 9704916372 JohnHarton ColoStateedu Review for Midterm 7 H Midterm II will be on Wednesday November 16 2005 in our classroom The exam will have four writeitout problems and it has the same weight in your final grade as the first midterm 7 15 As with the first midterm you may bring two pages of notes that you make 7 again no photocopying and no sharing of the note sheets You have to make your own The exam tests everything since the first midterm and that includes material from chapters 5 8 9 10 11 12 Since you will do chapter 12 so close to the exam we will not include it on this exam We also studied transformers from chapter 4 since the midterm but we will wait until the final exam as with chapter 12 to test that material MidtermH does draw upon all the material from this semester but strongly it emphasizes the work since 1Lidterm1 Here is a summary of the concepts we have learned since midterm1 1 made this summary by going back over my class notes and by looking at the assigned reading I wrote the exam using this summary your text and homework problems and lab circuits Chapter 5 sections 19 is about diodes and it is our first look at semiconductors With semiconductors there are two effective types of charge carriers electrons charge and holes charge The density of carriers in a semiconductor is far lower than the density of available electrons in a metal Silicon and Germanium are common materials for semiconductor devices Additives control the density of electrons and holes in diodes and other devices and the additives come from columns of the periodic table neighboring Si and Ge Socalled donors have an extra electron and acceptors lack an electron with respect to Si or Ge A ptype material has an abundance of holes due to doping with acceptors while n type has electrons as the majority carrier due to donor doping A diode has ptype material that changes abruptly to ntype across an interface This junction and the voltage across it produce the physics of interest The diode action explained in section 53 leads to the current versus voltage characteristics of the diode 7 the most important concepts for understanding circuits in this chapter Diodes can be used to rectify an AC voltage producing DC AC converted to DC is a common application and getting smooth DC output with reduced ripple is one of the challenges We studied several example circuits with diodes including a peak sampler39 voltage limiter39 clamps and a voltage multiplier Zener diodes have the interesting property of supporting a maximum reversed voltage and hence are useful in voltage limiters clamps and clippers Chapter 8 covers transistors and we studied sections 1 through 7 We mostly emphasized the npn transistor and its operation Again the pn junction of which there are two in the transistor is key You need to understand the transistor operation explained in the first sections of the chapter Can you explain the effect of the electric field at the two junctions when no voltage is applied and for when the transistor is turned on A given base current can imply a certain collector current with proportionality factor 3 7 but when does this relation not hold You had a lab exercise that made this clear 7 the transistor switch also see Technical Discourse 3 in the lab book and we had the homework quiz on this point The characteristic current vs voltage curves helped us understand the transistor just as the single iv curve did for the diode We studied the commonemitter amplifier in some detail homework problem and we know that it can be used to amplify the base voltage and the amplification depends on a couple of resistors not the particular 3 of the transistor We also worked on the emitterfollower which allows a source to drive more current than it could directly connected to the load homework too We saw how a couple of transistors could function as a logic gate lab exercise And we looked at a constant current source using a single transistor We mentioned FETs in class and how their operation is different from the npn transistor which we emphasized much more Chapter 9 introduces opamps and we covered sections 112 Operational amplifiers are quite complicated devices internally 20 transistors several resistors and capacitors but they have very simple rules of operation The opamp has two inputs called inverting and noninverting and one output node The basic characteristic for a bare opamp no feedback is that the output is Vcc if the noninverting we have called it v input is at higher voltage than the inverting input v and the output is 7Vcc if the inverting output is greater There is a linear range of some microvolts or millivolts over which the opamp output is proportional to the voltage difference VV but without feedback you cannot stay in this range Neither your book nor your lab manual show this plot but we drew it many times in class Feedback is the key to useful circuits the opamp and it is through feedback that we can keep the operation in the linear range We studied the inverting amplifier in detail and we learned how the feedback from the output to the inverting input works Another golden rule for opamps is that with negative feedback the device does what it must to keep the voltage difference between the two inputs at zero The other thing we need to know about ideal opamp operation is that no current enters the inputs 7 effectively infinite input impedance These rules lead easily to understanding the closedloop gain of the inverting amplifier Similarly straight forward are the noninverting amplifier and the summing and difference amplifiers all of which we went over in class We also looked brie y at opamp circuits that could differentiate or integrate a signal and you studied these in the lab We have lots of circuits and they are all pretty easy to understand if you know the opamp rules We analyzed a simple circuit that amplifies the input current independent of the load currenttocurrent amplifier and another that has an output voltage dependent on the input current currenttovoltage amplifier The Schmitt trigger uses positive feedback to change V when the opamp output changes state This has several uses one of which is to eliminate blinking of the output upon passage through a threshold because the threshold is changed by the positive feedback You built a circuit in lab that uses the Schmitt trigger combined with delayed negative feedback and result is the opamp oscillator The homework included a problem to find the oscillation frequency of such a circuit Real opamps have some limitations and we looked at these in class and in your text We learned how the very large but finite openloop gain affects the gain of the inverting amplifier and how to avoid any problems not too hard We examined the effective output impedance of the voltage follower39 this is a factor of the openloop gain A smaller than the bare output impedance of the opamp We also studied the input impedance of the voltage follower and the input impedance of the inverting amplifier also on the homework Chapter 10 covers oscillators and waveform generators You learned about the 555 timer and you used it in lab Chapter 11 is the introduction to digital electronics You will with Prof Wilson learn the basics of logic gates and Boolean algebra There are conventions for the circuit symbols that you need to know Understanding truth tables is the heart of the material This material is straight forward just follow the rules and your nose You will study the ipflop in lab 7 a very important concept You will also learn about different ways to code numbers binary octal etc
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