Bjt emitter follower voltage amplifiervoltage amplifier with r l, r o should be as small as possible what if a given amplifier configuration does not have small rwhat if a given amplifier configuration does not have small r o for example ce. Choosing the collector and emitter resistors the purpose of the collector resistor rc is to set the collector current ic as well as the emitter collector voltage vce. What are the advantages and uses of an emitter follower circuit. Transistor lab 2 emitterfollower science workshop p49 6 1996, pasco scientific dg 4. And yes, this resistance is indeed equal to re plus the resistance seen from the emitter at the base. The circuit shown next uses the v be shift up of a pnp emitter follower to partially cancel the v be shift down of an npn emitter follower. The common emitter amplifier circuit is shown below figure a. These are the mostly used ones with a number of applications.
Apr 02, 2017 this lecture presents emitter follower, that is common collector amplifier using exact and approximate analysis. Live tutors are available 24x7 hours for helping students in their emitter follower regulator related. Now, in an emitter follower transistor configuration as shown below, the load is connected at the emitter side of the transistor, that is between the emitter and the ground rail. The darlington emitterfollower input impedance is 35 re i kbdre 23. Output impedance seen by the load in this emitter follower. Class a npn emitterfollower amplifier analog devices wiki. Wu,uc berkeley emitter follower core ee105spring2008 lecture10,slide3prof. The emitter follower or common collector circuit configuration acts as a buffer, presenting a high impedance to the circuit that is driving it. The common emitter ce transistor amplifier configuration is widely used. Theres a handy trick for reducing the voltage offset between an emitter followers input and output.
The current gain of a commoncollector amplifier is equal to. This means that the emitter follower circuit provides an ideal buffer stage, and as a result it is used in many circuits where there is a need not to load a circuit like an oscillator or. So i would rather go for a buffer with a higher input impedance which is essential to isolate the circuit at the input of the buffer, from the circuit at its. Newest emitterfollower questions feed subscribe to rss newest emitterfollower questions feed to subscribe to this rss feed, copy and paste this url. Emitter follower circuit common collector configuration. Transistor emitter follower, common collector amplifier. Simulation of circuit performance with multisim and comparison with measured values. Select save as from the file menu to save your data. During the positive half cycle of v in, q 2 remains cutoff. By reading the above information you have got an idea about this concept.
In the transistor emitter follower circuit the output is taken from the emitter terminal. Emitter follower regulator, assignment help, zener voltage. A simple emitter follower is a great circuit element and will be found in most circuits. Now that we have established that you were thinking in the wrong area when you said one or two milliamps, you can work on things like the current gain of your emitter follower transistor to find out how. Wiring of bjt darlington emitter follower with and without. Therefore, the voltage at the output is the same as the voltage at the input.
Emitter follower or common collector amplifier circuit. And therefore this can be implemented in various circuit applications demanding a customized voltage controlled design. This article discusses the working of the common emitter amplifier circuit and its applications. It is called so because the transistor used is connected in an emitter follower configuration.
To work properly in an amplifier circuit a bipolar junction transistor bjt must be properly biased and operate in the active mode. Emitter follower article about emitter follower by the. From the voltage waveforms for the ce circuit shown in fig. Comparing this with the input resistance of the commonemitter circuit, we see that the emitter follower has much higher input resistance. The analysis uses a basic emitterfollower circuit, using the ubiquitous 2n2222 transistor a. You are looking the resistance seen from the load resistance perspective by looking into emitter terminal seen from the emitter into the bjt. The ac voltage gain of cc amplifier is calculated as e v ee r a rr 1. Emitter follower accessscience from mcgrawhill education. Lab 8 common collector or emitter follower amplifier prelab.
As the input signal green, top drops below vbe, the output signal red, bottom is clipped to 0 v b. The emitter follower configuration is frequently used for impedance matching and to increase the current gain. The emitter follower or common collector circuit is widely used in amplifier configuration of bipolar junction transistors bjts with gain of unity or less. Such a circuit is also named an emitter follower voltage regulator. Achieving unity gain using either source follower or emitter follower isnt possible unless you have an absolutely ideal current source at the sourceemitter, which isnt usually the case. The emitter follower bellow cannot follow the base voltage vb after some point. Mar 11, 2017 an emitter follower, or common collector, configuration usually has either a current source or resistor supplying current into the emitter. When we place the emitterfollower on the output of the ce amplifier from the class a npn commonemitter amplifier lab, we have nonzero r s, and need to include it in out calculation of r o we will see a small voltage divider loss when driving the 47. Find the qpoint values icq and v ceq of this circuit if re rl 100 assume vs to be an ideal ac voltage source. Emitter follower circuit common collector configuration problem 1 video lecture from bipolar junction transistor chapter of analog electronics subject for electronics engineering students.
The analysis uses a basic emitter follower circuit, using the ubiquitous 2n2222 transistor a. Perform dc and smallsignal analysis on an npn emitter follower stage. In applications where small signal voltages must be amplified. With a single emitter follower transistor operating in class a, you will need. The commoncollector amplifier bipolar junction transistors.
The output voltage on a commoncollector amplifier will be in phase with the input voltage, making the commoncollector a noninverting amplifier circuit. Avoid clipping in emitter follower with accoupled resistive. Since an integrated circuit is constructed primarily from dozens to even millions of transistors formed from a single, thin silicon crystal, it. Common emitter configuration commonly used in lownoise amplifiers. The collectoremitter voltage at the operating point is then vce vbattery 3 12 3 4 v.
The advantage of this circuit is that the transistor can provide current and power gain. The opencircuit voltage g ain, a v, of the emitter follower amplifier can be c alculated using the following equation since r e is typically much larger than r e, the equation can be. Experiment 6 transistors as amplifiers and switches our final topic of the term is an introduction to the transistor as a discrete circuit element. The common collector circuit configuration is more widely known as the emitter follower and it provides a high input impedance and a low output impedance. To familiarize with the concept of input and output impedance of a circuit. The commoncollector amplifier is also known as an emitterfollower. Common collector configurationemitter follower using darlington pairgain and input. To design, build, and test an emitterfollower amplifier using a 2n3904 npn transistor, with an input resistance of at least 1 k.
Emitter follower regulator topic is not easier to learn without any external help. Voltage regulators,circuits,types,working principle. Newest emitterfollower questions electrical engineering. The voltage divider at left is a poor voltage source because it is so strongly affected by the value of the load resistor. The input is applied at the emitter and the output is taken at the collector. Since an integrated circuit is constructed primarily from dozens to even millions of transistors formed from a single, thin silicon crystal, it might be interesting and instructive to. Experiment 6 transistors as amplifiers and switches. The emitter follower circuit which was just discussed lacks to meet the requirements of the circuit current gain a and the input impedance z. If care is not taken to run it at sufficient current, however, one can find it causes terrible distortion on transients due to capacitance on the emitter figure 2. The emitter follower configuration is frequently used for. The following few example circuits show how typically an emitter follower circuit can be used in circuits. What are the advantages and uses of an emitter follower.
This file is licensed under the creative commons attributionshare alike 3. Empirically explore the effect of changing the load resistor. An emitter follower configuration gives you the advantage of getting an output that becomes controllable at the base of the transistor. The output voltage vout however stops following vb at some particular. The same voltage divider with the transistor buffer at right will supply power to keep the voltage constant over its range of operation. The purpose of biasing is to establish a qpoint about which variations in current and voltage can occur in response to an ac input signal. Emitterfollower configuration part 1 topics covered. When this happens the emitter is not able to acquire a 0v potential, and the bjt is unable to turn on with a regular 0. While doing the experiment do not exceed the ratings of the diode. This capacitance may be the collectortosubstrate capacitance of the current source supplying the emitter current. Emitter follower and darlington amplifier are the most common examples for feedback amplifiers.
Experiment 2the emitterfollower amplifier 1 free download as pdf file. To obtain measured values of voltage amplification av, input impedance zi and output impedance zo. An emitter follower also known as a common collector amplifier is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer. Simulation of amplifier circuits studied in the lab using any available simulation. Measuring inputoutput impedance emitter follower all. In this project, we will show how to build an emitter follower circuit. The circuit consists of an npn transistor and a zener diode. An emitter follower has a slight loss in voltage gain but makes up for it in current. Common emitter amplifier working principle and its. The voltage gain is approximately equal to unity and output voltage is in phase with the input voltage. Aug 24, 2019 now, in an emitter follower transistor configuration as shown below, the load is connected at the emitter side of the transistor, that is between the emitter and the ground rail.
As shown in the figure below, the collector and emitter terminals of the transistor are in series with the load. It is a mirror image, so to speak, of the input voltage. Achieving unity gain using either source follower or emitter follower isnt possible unless you have an absolutely ideal current source at the source emitter, which isnt usually the case. In a circuit if the output voltage is approximately equal to the input voltage, such a circuit is known as emitter follower. Evaluate the benefits of using of transistors to design stiffer electronic circuits. Choosing the collector and emitter resistors the purpose of the collector resistor rc is to set the collector current ic as well as the emittercollector voltage vce. H2lthe base bias can be represented by its theveninequivalent hr b r b1 eer b2 l emitter follower. Unlike the common emitter amplifier, the output voltage of the common collector amplifier is in phase with the input voltage. The input and output of an emitter follower are the base and the emitter, respectively, and the collector is at ac zero. An emitter follower, or common collector, configuration usually has either a current source or resistor supplying current into the emitter. It provides large voltage gain typically tens to hundreds and provides moderate input and output impedance. The output resistance is the parallel combination of and the resistance of the circuit to the left of the emitter of the transistor including, which can be found as the ratio of the opencircuit voltage with and the shortcircuit.
An emitter follower circuit is a transistor circuit in which the voltage at the emitter follows the input voltage. The commonemitter ce transistor amplifier configuration is widely used. Experiment 2the emitterfollower amplifier 1 scribd. The collector emitter voltage at the operating point is then vce vbattery 3 12 3 4 v. The commoncollector cc or emitter follower ef transistor amplifier configuration is used primarily for impedance matching operation. The biasing analysis is similar to that for single transistor except that two v be drops are to be considered. Upon completing the experiment, students should switch off the power supply and then remove. In other words, rc helps to set the transistor at the operating point of the amplifier. An emitter follower is often used this way, since this avoids the need to bias the transistor and avoids the coupling capacitor. The result is that emitter current of the first transistor is the base current of the second transistor. In its behavior, the emitter follower is analogous and very similar to the source follower in metaloxidesemiconductor mos circuits. The emitter follower or common collector transistor configuration is widely used in many applications. H1lin this circuit r c is at ac ground at both ends.
Common emitter amplifier working principle and its applications. Measure the characteristics of an emitter follower. A circuit that uses a commoncollector transistor amplifier stage with unity voltage gain, large input resistance r i, and small output resistance r o see illustration. Lecture 10 emitter follower common collector amplifier. Unlike the common emitter amplifier, the output voltage of the common collector amplifier is in phase with the input. The voltage gain of the emitter follower is less than one, but it has reasonably high current gain. There is usually no collector load resistor, with the collector connected directly to the supply. To determine input impedance, i have the 10k resistor and am measuring the voltage on both sides of it. Common emitter amplifier circuit elements and their functions. The commoncollector cc or emitterfollower ef transistor amplifier configuration is used primarily for impedance matching operation. May 25, 2018 theres a handy trick for reducing the voltage offset between an emitter followers input and output.
Common emitter amplifiers are also used in radio frequency transceiver circuits. The ac signal voltage gain is defined as a v v o v i where v o and v i can both be rms, peak, or peakpeak values. Science workshop transistor lab 2 emitterfollower dg 1996, pasco scientific p49 1 experiment p49. Im simulating this circuit in ltspice see attachment. However, theres a note in the book that a base resistor is needed to omit any oscillation. In its behavior, the emitter follower is analogous and very similar to the source follower in. Turn off the power switch on the back of the power amplifier. Emitter follower article about emitter follower by the free. In many applications, a bidirectional emitter follower circuit that can source and sink currents with equal ease is required, and this action can be obtained by using a complementary emitter follower configuration in which npn and pnp emitter followers are effectively wired in series. A problem suffered by the simple emitter follower can be seen when it drives a capacitive load. The rise time of the output can be relative fast as the emitter current is limited only by beta times the base current that can be supplied by the signal source driving the base.
Permission is granted to copy, distribute andor modify this document under the terms of the gnu free documentation license, version 1. Emitter follower is a case of negative current feedback circuit. Comparing this with the input resistance of the common emitter circuit, we see that the emitter follower has much higher input resistance. The darlington emitterfollower has a higher input impedance than that of an emitterfollower. The emitter follower has a high input impedance and low output impedance, which is almost equal to the emitter resistance. It rovides voltage gain near unity, high input and low output impedance. Hi, so, im learning emitter follower by building a circuit that is described in learning the art of electronic book in the lab 3 chapter. Emitter follower or common collector amplifier circuit this tutorial will help you to build and simulate a more complex circuit. In the book, theres an emitter follower circuit to demonstrate the clipping effect and how to remedy it. This is an emitter follower or buffer amplifier circuit, where the output is simply equal to the input minus a diode drop about 700mv.
The follower circuit is often used as a buffer stage for this reason. In order to achieve some increase in the overall values of circuit current gain and input impedance, two transistors are connected as shown in the following circuit diagram. Analysis of emitter follower core impact of source resistance impact of early effect emitter follower with biasing reading. I would opt for a source follower over an emitter follower mainly because it has a much higher input impedance. Emitter follower circuit has a prominent place in feedback amplifiers. The emitter follower common collector amplifier assumptions. An emitter follower can serve as a buffer for a voltage source.