In the transistor emitter follower circuit the output is taken from the emitter terminal. Introduction to electronics xvi 1 i use the word supposedly because, in my view, the official rewards for textbook authoring fall far short of what is. The basic transistor amplifier circuit is indicated below. The input resistance r i of a cc amplifier or emitter follower is very high, of the order of hundred of kiloohms while its output resistance is very low, of the order of tens of ohms. H1lin this circuit r c is at ac ground at both ends. The collectorto emitter voltage is given by vce vc. Power amplifier 120vac staner amp tef pcb electronic circuit. In electronics, a common collector amplifier also known as an emitter follower is one of three basic singlestage bipolar junction transistor bjt amplifier topologies, typically used as a voltage buffer in this circuit the base terminal of the transistor serves as the input, the emitter is the output, and the collector is common to both for example, it may be tied to ground. The current mirror from activity 5 is now substituted for the emitter load resistor to fix the amplifier transistor emitter current. 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. The voltage gain is approximately equal to unity and output voltage is in phase with the input voltage.
Bjt ampli er circuits university of california, san diego. In this circuit a zener diode is placed at the base of the transistor to clamp the voltage at the base to vz of the zener. There are additionally three capacitors but they do not play a role in the basic transistor amplifier design which mainly involves setting dc voltages. Common collector amplifier or emitter follower circuit and. 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. To design, build, and test an emitter follower amplifier using a 2n3904 npn transistor, with an input resistance of at least 1 k. H2lthe base bias can be represented by its theveninequivalent hr b r b1 eer b2 l emitter follower. Assuming the same bjt parameters and using a dc analysis as in example 2, 1, we get v be 0. Npn voltage follower with current source biasing suitable for integrated circuits. Bjt amplifiers 6 chapter outline 61 amplifier operation 62 transistor ac models 63 the common emitter amplifier 64 the commoncollector amplifier 65 the commonbase amplifier 66 multistage amplifiers 67 the differential amplifier 68 troubleshooting device application chapter objectives describe amplifier operation discuss transistor models. 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. Linearity of such an input stage is not easily compared to the more traditional di erential pair because of its fundamentally di erent operation. Your author states that the load for an ef amplifier is small and often.
Also called a darlington configuration, emitter followers have a gain of unity. Wu,uc berkeley emitter follower core ee105spring2008 lecture10,slide3prof. This pcb layout for power amplifier staner tef three emitter follower fix and complete pcb layout pdf you can download at the end of this post. It is called a common emitter amplifier since the emitter is common to both the input circuti and the output circuit. Analysis of emitter follower core impact of source resistance impact of early effect emitter follower with biasing reading. As we discussed in our previous article, there are three transistor configurations that are used commonly for signal amplification i. The emitter follower or common collector circuit is widely used in amplifier configuration of bipolar junction transistors bjts with gain of unity or less. The emitter follower configuration is frequently used for impedance matching and to increase the current gain. The wiki page on common collector topology that the picture in the question comes from says this.
Coates 2007 2012 power amplifiers introduction to power amplifiers power amplifiers amplifier circuits form the basis of most electronic systems, many of which need to produce high power to drive some output device. Such a circuit is in fact the rst stage of the 741 opamp. This type of configuration is called common collector, cc because the collector terminal is effectively. Thus, the emitter may be said to follow the input signal and hence the name emitter follower. Amplifiers with negative feedback questions and answers pdf free download also objective type mcqs interview questions 2 mark important lab viva manual amplifiers with negative feedback questions with answers. I am trying to find the input resistance of this bj common emitter amplifier. Differential amplifier stages large signal behavior general features. The advantage of this circuit is that the transistor can provide current and power gain. To an ac signal this looks like the collector is connected to ground. The emitter follower transistor amplifier has a very straightforward circuit. Class a npn emitterfollower amplifier analog devices wiki.
In our previous discussion, we learned that a common emitter amplifier is most widely used amplifier circuit and common base amplifier is least widely used amplifier whereas a common collector amplifier is moderately used amplifier in this article, you will be able to learn and understand the working of common collector amplifier, their characteristics, and. Thus the collector terminal is common to both the input and output circuits. This is also called the common drain cd and is analogous to the common collector a. High frequency response of the ef cc amplifier the generic circuit for the emitter follower common collector amplifier is given to the left below and the high frequency small signal circuit is shown below and to the right figures 10. This power amplifier can be supplied with 120vac power supply circuit and can deliver output up to 2000w power rms with using a powerful power supply, this power amplifier specified for pa amplifier. Common collector emitter follower transistor amplifier basics. This lecture presents emitter follower, that is common collector amplifier using exact and approximate analysis. The collector is connected tied to a dc power supply. Lecture 10 emitter follower common collector amplifier. The common collector amplifier is another type of bipolar junction transistor, bjt configuration where the input signal is applied to the base terminal and the output signal taken from the emitter terminal. Emitter follower circuit stabilized to prevent oscillations filed oct. This observation leads us to the first possible improvement in the emitter follower. Transistor emitter follower, common collector amplifier. The base is connected to the previous stage, and often this may be directly connected as this can save on additional bias resistors which lower the input impedance and hence increase the loading to the previous stage.
The datasheet for the lm386 amplifier shows that its output at clipping with a 9v supply is 450mw into 8 ohms with low distortion. Common emitter bjt amplifier design current mirror design. Your basic output stage is the double emitter follower a npn pair q4, q6 for positive output currents and a a pnp pair q5,q7 for negative output currents. A current mirror will sink a more or less constant current over a. These are the mostly used ones with a number of applications.
One of the application in which i have personally used emitter follower circuit is a discrete voltage regulator. R b serves no purpose except to provide a path for the base current. In other words, inside a linear integrated circuit, current source biasing is usually preferred over the use of a resistor. The analysis uses a basic emitter follower circuit, using the ubiquitous 2n2222 transistor a. Emitter follower is a case of negative current feedback circuit. The need for a current source in an emitter follower. If we try to couple the output of our ce amplifier directly into this load resistance, we may overload the amplifier and a substantial drop in gain will occur. Emitter follower and darlington amplifier are the most common examples for feedback amplifiers. Because the dc bias circuits are the same as for the common emitter ampli. In the source follower sf configuration, the ac input is applied at c g, the ac output is taken at c s and the drain is either connected to a dc voltage supply with or without c d. Pcb layout for power amplifier staner tef three emitter follower fix and complete pcb layout pdf you can download at the end of this post.
How to connect common emitter with emitter follower to. A classab amplifier like an lm386 is much more efficient and works very well. P esquaredr 12 esquared8 e 2 thats 2 volts rms you will need 5. This file is licensed under the creative commons attributionshare alike 3. As the input signal green, top drops below vbe, the output signal red, bottom is clipped to 0 v b. Emitter follower circuit has a prominent place in feedback amplifiers. With a single emitter follower transistor operating in class a, you will need. Common collector amplifier basic electronics tutorials. This is an emitter follower or buffer amplifier circuit, where the output is simply equal to the input minus a diode drop about 700mv. Emitter follower aka common collector amplifier a typical emitter follower amplifier is shown in fig. Emitter follower or common collector amplifier circuit this tutorial will help you to build and simulate a more complex circuit.