Emitter follower circuit diagram

In electronics , a common collector amplifier also known as an emitter follower is one of three basic single-stage 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 reference or a power supply rail , hence its name. The analogous field-effect transistor circuit is the common drain amplifier and the analogous tube circuit is the cathode follower. The circuit can be explained by viewing the transistor as being under the control of negative feedback.

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• A Darlington emitter follower circuit is sometimes used in the output stage of TTL gate to _____.
• 9V-12V Negative Voltage Regulator using PNP Emitter Follower
• Emitter-Follower Audion Schematic Circuit Diagram
• Darlington Emitter Follower and Amplifier
• Darlington Emitter Follower and Amplifier
• What is Common Source Amplifier : Working & Its Applications
• Follow The Leader - Voltage Followers & Buffers

WATCH RELATED VIDEO: Darlington Emitter Follower - Buffer With Just Transistors - Simply Put

A Darlington emitter follower circuit is sometimes used in the output stage of TTL gate to _____.

There are many systems which require the use of audio filters of miniature size. Airborne systems such as airborne radar systems, telemetering systems and interplane communication systems are typical examples. Miniature filters also find application in similar shipboard and land based electronic systems and wherever size, weight or cost is a factor to be considered in the design.

Low frequency passive filters have the disadvantage that relatively large inductance values are required if relatively high input impedance to the filter is desired. As a result, low frequency passive filters require relatively large amounts of space and are relatively heavy and expensive.

Attempts have been made to overcome these disadvantages of passive filters by replacing the inductors by a combination of capacitors and active elements so arranged as to present an inductive impedance at the output terminals thereof. Still other attempts have been made to increase the apparent inductance of a small physical inductor through the use of active circuits.

Some success has been achieved in reducing the volume of these types of active filters below that of the passive filter of similar passband characteristics. However active filters of the type mentioned have a limited dynamic range, a relatively high insertion loss and a relatively large power consumption. The characteristics of the filters are highly dependent on supply voltage and temperature.

The cost of an active filter may be of the order of ten to twenty times that of the passive filter it replaces and much more time and labor is required in designing the filter. It is an object of the present invention to provide a novel active filter circuit which occupies much less space than equivalent active or passive filters. Still another object of the invention is to provide a highly stable active filter network having an insertion loss and a dynamic range comparable to that of a passive filter.

Still another object of the invention is to provide a novel active filter circuit which has relatively few parts and requires very little power. In general, the invention comprises two or more filter sections connected in cascade by means of impedancereducing electron amplifier stages inserted between adjacent filter sections.

In certain preferred forms of the invention the filter sections may comprise simple inductorcapacitor networks. The impedance-reducing electron amplifier stages may comprise transistor-emitter follower circuits. For a better understanding of the present invention together with other and further objects thereof reference should now be made to the following detailed description which is to be read in conjunction with the accompanying drawings in which:.

The circuit of Fig. Additional emitter-follower stages 10 form the input and output circuits of the cascade arrangement. Each emitter-follower stage may comprise a transistor 14, a load resistor 16 and a base resistor The collector of each of the transistors 14 is connected to one terminal of a source of supply potential which is represented in Fig.

The other terminal of the supply source may be at ground potential. Thus the source is connected across the series combination of transistor 14 and load resistor The polarity of terminal 22 of the source will depend on the type of transistor employed.

Networks 12 are shown as three terminal networks in which the input terminal 26 is connected to the emitter of one transistor 14 while the output terminal 28 is connected through the base resistor 18 to the base of the following transistor The common terminal 32 of such network 12 is shown connected to a source of base bias potential schematically represented by terminal The purpose of bias source 34 is to supply the usual operating bias for the base of the following emitter-follower circuit Therefore, in embodiments ofthe invention employing a four-terminal network in place of one or more of the three terminal networks 12, the second input terminal may be connected to ground and the second output terminal may be connected to source The first emitter-follower stage 10 is provided with input connections 40 to which the signal to be processed may be supplied.

The first stage 10 is provided with a source of bias potential 42 through an isolating resistor 44 and base resistor In practice, one common bias source may be provided in place of the individual sources 42 and An output connection 46 may be provided at the emitter of the final emitter-follower stage The two networks 12 shown in Fig.

In most instances these two networks will have quite different pole-zero configurations in order to obtain the desired overall passband for the filter networks. The emitterfollower stages provide suflicient isolation between adjacent networks so that the reaction of one network on the other may be, in general, ignored.

The isolation between adjacent networks 12 is further enhanced by placing the poles of one network 12 as far as possible from the poles of the adjoining network. The impedance step down provided by the emitter-follower stages 10 permits the elements of similar frequency selective networks in different parts of the cascade arrangement to have impedance values of the same order of magnitude.

Since it is not necessary to change the physical size of successive filter elements to obtain a progressive change in the impedance levels of the selective circuits, the elements of all of the frequency-selective circuits may be of relatively small physical size. Only two networks 12 have been shown in Fig. Additional emitter-follower stages 10 may be added to separate each added network from the other network in the cascade arrangement. As indicated above, the relatively simple pole-zero techniques may be employed in designing a particular passband in place of the much more complicated calculations required by passive filter theory.

The use of emitter-follower stages yields voltage gains approaching unity in each section. Since the collectors of the transistors are at A. The use of emitter followers causes the response within the passband to have excellent linearity.

The circuit disclosed is substantially independent of changes in supply voltages or temperature over wide ranges. The circuit is well adapted to potting or.

Only two power terminals are required in addition to the necessary input and output terminals. The high input impedance and low output impedance of the emitter-follower stage, together with the isolation between adjacent networks 12, makes it possible to employ inductors of smaller size than can be employed in equivalent passive filters. A typical filter constructed in accordance with the teachings of the present invention may have a volume approximately one-eighth that of the corresponding passive filter and less than one-third that of the equivalent active filter employing negative impedance converters.

This typical filter requires only about one-tenth the number of transistors and one-tenth the input power required by active filters employing negative impedance converters. This smaller, less expensive filter of the present invention may be constructed to have a dynamic range of 75 db as compared to db for a passive filter and only 35 db for active filters employing negative impedance converters.

The insertion loss of the filter of the present invention can be made as low as 0. Components in Fig. As shown in Fig. The output terminal of the network is at the junction of capacitor 54 and inductor As indicated above, it is not necessary to arrange the network 12 into a T or 1r network having the same input and output impedance. Each emitterfollower stage functions as a low impedance source for the network which follows it and a high impedance load across the network that precedes it.

Other forms of passbands can be selected by applying well known, pole-zero techniques to the selection of the characteristics of the individual networks. Transistor-emitter follower circuits are ideally suited for use in the circuits just described because of their small physical size, low power drain and desirable input impedance versus output impedance ratio. However it lies within the scope of the present invention to employ other forms of impedance-reducing amplifier stages, particularly vacuum tube cathode-follower circuits.

While the invention has been described with reference to the preferred embodiments thereof, it will be apparent that various modifications and other embodiments thereof will occur to those skilled in the art within the scope of the invention.

Accordingly I desire the scope of my invention to be limited only by the appended claims. An audio frequency filter in accordance with claim 2 wherein said means coupling said output terminal of said filter section to the base of the following transistor comprises a second decoupling resistor.

A filter in accordance with claim 4 wherein said means coupling said intermediate point on said series circuit to the base of the following transistor comprises a second decoupling resistor. A filter in accordance with claim 6 wherein said means coupling said second terminal of said capacitor to the base of the transistor in the following stage comprises a second decoupling resistor.

USA en. Two input-two output logic circuit for electronic selectors using three transistor configuration.

Bandpass transistor amplifier with automatic gain control and active isolating means. EPB1 en. SEB en. USB2 en. GBA en. EPA2 en. Circuit arrangements employing active elements therein functioning as circulators,gyrators,inductors or filters. Afc circuit arrangement for fine-tuning the sine-oscillating circuit of a horizon tal oscillator in television sets.

Leoni et al. Feedback amplifier utilizing a feed forward technique to achieve high direct currentgain and wide bandwidth.

9V-12V Negative Voltage Regulator using PNP Emitter Follower

In electronic circuits, amplifiers are used to increase the strength or amplitude of the input signal without any phase change and frequency. Amplifier circuits are made up of either FET Fied Effect Transistor or normal bipolar junction transistor -based on their 3 terminals. The advantage of amplifier circuit using FET over BJTs is used as small-signal amplifiers because they produce high input impedance, high voltage gain, and low noise in the input signal. FET is a voltage-controlled device with three terminals -source, drain, and gate. Based on these terminals, FET is divided into 3 amplifier configuration that corresponding to 3 configurations of Bipolar transistors. They are common-source, common drain source-follower , and common-gate amplifier circuits.

Emitter-Follower Audion Schematic Circuit Diagram

Although one is npn and the other is prim the devices are selected to have similar parameters, so they are complementary transistors. The circuit is termed a complementary emitter follower. A single-transistor emitter follower is essentially a small-signal circuit, because large signals can reverse bias the transistor base-emitter junction when the input polarity is opposite to the transistor V BE polarity. An npn emitter follower might not correctly reproduce the negative-going portion of a large signal, while a pnp emitter follower might not reproduce the positive-going portion. Complementary emitter followers have similar signals applied simultaneously to both device bases, as illustrated. Transistor Q 1 conducts during the positive half-cycle of the signal, and it pulls the output voltage up to follow the input. During this time, Q 2 base-emitter junction is reverse biased. For the duration of the negative half-cycle of the input, Q 1 base-emitter junction is reversed and Q 2 conducts, pulling the output down to follow the input. Thus, the complementary emitter follower is a large-signal circuit with the low output impedance typical of emitter followers. Skip to content.

Darlington Emitter Follower and Amplifier

Simple Voltage Follower Circuit Using op amp designed to give unity gain output. We know voltage follower circuit will give the output same as input signal but the output gain only increase. Voltage follower amplifier can also called as Unity gain amplifier or Buffer amplifier. We commonly using IC LM as a operational amplifier and the following circuit also designed by using op amp IC is a dual inline packed 8 Pin integrated circuit.

Darlington Emitter Follower and Amplifier

A shortwave audion receiver using only two transistors and a single 1. Just add an active PC loudspeaker for very convincing performance. This produces a capacitive voltage divider, enabling the transistor to operate as a three-point oscillator, also known as a Hartley oscillator. Only a minute amount of emitter current is required to go into oscillation. The trimpot trimmer potentiometer is used to adjust the audion for AM reception so that it does not quite oscillate immediately before oscillation sets in , for CW telegraphy with keyed carrier and SSB single-sideband reception it is set slightly higher. Decoupling and amplification of the audio signal is handled by the second transistor.

What is Common Source Amplifier : Working & Its Applications

A Darlington pair configuration has high input impedance and low output impedance. Thus it is used as a buffer circuit for impedance matching with the circuits that require high input impedance at the input. In addition to providing high input impedance, the Darlington pair also provides high current gain. Hence a Darlington emitter follower circuit is sometimes used in the output stage of the TTL gate to increase speed. Start Learning English Hindi. This question was previously asked in. Start Now. Explanation: 1.

Follow The Leader - Voltage Followers & Buffers

The prime concerns of the electronic systems are Stability and Accuracy. To maintain these key factors, some part of the output is connected back to the input of the system, which is called feedback. The control systems are classified as 2 types based on the feedback connection, such as closed loop systems and open loop systems. Based on the nature of feedback, the closed loop systems are again classified as 2 types, they are Positive feedback systems and Negative feedback systems.

There are many systems which require the use of audio filters of miniature size. Airborne systems such as airborne radar systems, telemetering systems and interplane communication systems are typical examples. Miniature filters also find application in similar shipboard and land based electronic systems and wherever size, weight or cost is a factor to be considered in the design. Low frequency passive filters have the disadvantage that relatively large inductance values are required if relatively high input impedance to the filter is desired. As a result, low frequency passive filters require relatively large amounts of space and are relatively heavy and expensive. Attempts have been made to overcome these disadvantages of passive filters by replacing the inductors by a combination of capacitors and active elements so arranged as to present an inductive impedance at the output terminals thereof.

Many electronic circuits, including voltage dividers and filters, produce signals that sag when current is drawn. An Emitter-Follower uses a transistor to reduce this sag by a factor of The following information is adapted from the lab materials of an electronics course at Pomona College. Most signals and voltage sources are imperfect. Generally, when we try to draw current from a voltage source, the voltage decreases. This decrease in voltage is called sag. Sag can cause significant problems in multi-stage circuits where later stages depend on receiving a stable voltage.

In this post, I am going to show two Negative Voltage Regulator circuit ideas. Before we use the just positive regulator as Simple DC regulator using transistor and Zener. The output voltage of this circuit is 12V.