Audio amplifier circuit using bjt


  • Common Emitter Amplifier Circuit Working & Its Characteristics
  • Transistor Amplifier | It’s Important types | Variant such as BJT, FET
  • Chapter 6 Transistor (BJT) Amplifiers – Electronic Circuit Analysis
  • Simple Single Transistor Audio Amplifier Circuit
  • Audio Amplifier- A Brief Outlook to Its Many Types
  • Electronic – My BJT audio amplifier circuit isn’t working as expected
  • Mini Audio Amplifier Circuits
  • Common Emitter Amplifier Circuit Working & Its Characteristics

    ClassAB power amplifiers can also be used but ClassD is more preferred because of its light weight and low heat dissipation characteristics. Audio amplifiers are used in many application from Radio wave transmitter, Hi-fi devices, Home audio systems, talking toys, Robots and even in military as an acoustic weapon.

    What is Audio Amplifier? A basic power amplifier that is designed to take input as the low strength audio signal and generate the output signal that consists of the high strength value. This process of amplification is utilized in the various domains where an electical signal is converted to an acoustic signal. This type of amplifiers is known as audio amplifiers. Any circuit which processes the audio signal has the audio amplifier both at the input and also at the output.

    For example, if a microphone receives a sound wave input signal it need a pre-amplification of the signal before processing it further and similar before sending an electrical signal to a speaker it needs to be amplified. Audio Amplifier Circuit The circuit of the audio amplifier consists of a transistor a device to apply the input signals and a speaker at the output. The transistors are connected based on the necessity. The important factors that need to be considered while designing a audio amplifier is gain,noise, frequency response and distortion.

    Higher the gain higher will be the distortion and noise however a negative feedback would reduce the gain of the amplifier. This amplification of the audio signals is carried out in various stages. Based on the criteria of the hall, infrastructure, and the impedance value the amplification of the signals takes place.

    The power generated at the output of these amplifiers depends upon its utility. The input signal is applied with the help of any mike and as it reaches the transistor the movements of majority and the minority carriers takes place.

    If the transistor is of n-p-n-type, in that case, the connections of the supply are provided in such a way that the width of the depletion region should be less which indicates that the transistor should be in fully conducting mode. The amplifiers can be designed with multiple transistors in it.

    Based on these movements of the carriers the signal reaches to its destination. This process signal reaching to the destination with the replica of the input signal but boosted in terms of strength is known as amplification.

    This is just about the single stage of the amplification based on the criteria this number of stages varies. The stages are dependent on the amplification strength value. In this way, the amplifier works.

    Based on the criteria of amplification it may vary but the factors called impedance, power etc…remains same. Applications There are various usages of audio amplifiers. Some of them are listed as follows: In the sound systems, these amplifiers are most widely used. In various instruments that relate to music, these amplifiers are installed.

    In the radio signals broadcasting these amplifiers are used. The signal transmission for long-distance communication is the most amplifiers that are utilized. For the wireless transmission of the signals, audio amplification is required. Nx Audio Amplifier This Nx audio amplifier is a type of amplifier that is good enough at amplifying the strength of the sound signals.

    This amplifier comes in various versions. Each version can be designed from the various manufacturers. It supports class-AB amplifiers. Each type of supports two channels.

    The various versions possess various maximum power varying capabilities. It also has various impedance values. Nx Audio Amplifiers In this way, one can describe that it is an amplifier that relates to sound amplification with various parameters of sound like power varying, impedance varying in it.

    Lm Audio Amplifier This is a kind of operational amplifier that is designed to perform certain tasks like if the input signal applied to the amplifier then it gets modulated ten times, a hundred times and even better. It is a basic amplifier in the form of a chip that consists of 8 pins. The starting pin that is 1 and the pin, at last, that is 8 denote the gain values of that particular amplifier.

    This gain value can be adjusted by connecting a capacitor to the circuit. Lm Audio Amplifier A potentiometer is connected to it so that one can control the volume of the amplifier. In this kind of amplifiers, the distortion of the amplified signal will be low.

    This kind of audio amplifier chip operates on the battery. As the pins that are used in this chip can alter and manage the gains of the amplifier this can act as a flexible amplifier. Hence Lm can be used in various applications of portable amplifiers of audio, ultrasonic sensors, and the power converters, etc… Audio amplifiers are the basic power amplifiers that can be of various types like it is designed in various versions.

    There are various parameters technically and even the parameters related to infrastructure also affect the audio amplification. The audio amplifiers are designed in the form of chips and various sizes. Many manufacturing companies designs this set of amplifiers based on the criteria provided by the client.

    The best practical example of the audio amplifier is the siren that has the capability of increasing the strength of the applied signal and give an output with the maximum strength of the signal. Now can you give another practical example where lively you can notice the application of the audio amplifier?

    Transistor Amplifier | It’s Important types | Variant such as BJT, FET

    These are the requirements of the circuit: Input signal: mV It's the output of my iphone's microphone. I can choose to feed enough my circuit. Here's the circuit: I'm having troubles with impedance matching. Can anyone tell me how to calculate the input impedance, output impedance and the gain of the power amplifier stage? I want to calculate exactly to ensure that the voltage is not dropped a lot on the output impedance of the CE stage and the power amplifier stage.

    In other words, I want to maximize the voltage dropped on the 4 ohms Rload. My calculations seem to be wrong, which result in 0. But I want to expand on the original answer. My apologies it has grown so long. Keep in mind that I'm just a hobbyist who enjoys learning. There are a variety of different types of audio amplifiers.

    Most of them today will be based upon ICs, as they are quite common, cheap, and perform well. Even that part is now obsolete and, for example, the TDAA is a replacement for it. This is one of the wonderful things that ICs can provide, which are twice as difficult to achieve with discrete parts and relatively easy with ICs.

    In addition, there are class-D and beyond amplifiers in common use in ICs today. But this is about doing an audio amplifier design with discrete active devices. Performing an audio amplifier design with discrete parts teaches many of the skills needed for general discrete part design. So it's worth a moment. So the simpler class-A design is used here for parsimonious reasons.

    If you are interested in delving further, there are some really good books available. The purpose here is more about performing a simple audio amplifier design, using discrete parts, for educational purposes.

    But it has a better chance at being understandable. I also intend to stay with single-rail voltage supplies, rather than bipolar, for pedagogical reasons. Just FYI. Output Stages There are at least two kinds of output stages that I won't consider. These are the common-emitter and common-collector emitter-follower forms: simulate this circuit — Schematic created using CircuitLab Neither of these are acceptable in most audio amplifier circumstances.

    This is partly because, while there is an active device for one drive quadrant, the opposing drive quadrant is supported only by a passive collector or emitter resistor resulting in distortion, or worse, almost no useful output.

    Only in very rare circumstances, and never in audio situations I'm aware of, is this okay. Most situations require an active device in both drive quadrants. The above problem can be fixed by using two active devices, one for each of the two needed quadrants. But then you'd need to "think upside down. Just be aware that circuits often can be arranged either way. Although I will focus on class-A output stages here, it's worth a moment to see the slight differences involved in a class-AB output topology using complementary BJTs: simulate this circuit The class-AB output stage is less power-hungry: In the class-A case, both BJTs carry the full quiescent current when inactive.

    In practice, it will be quite a bit less than that but always better than class-A operation. In fact, there are perhaps a dozen arrangements I'm at least semi-familiar with, each offering various advantages. These include dual positive and dual negative rails supporting stacked output sections for improved efficiency handling both low and high power outputs with the same circuitry.

    I won't cover any of that here. Just pointing out that there is a lot to learn in class-AB audio output stages, if you want to be comprehensive. By comparison, class-A power output stages are relatively easier to understand. Returning to the class-A output stage, the above examples expose two BJT base connections. So does the class-AB shown above. For class-A, we can repair that by inserting a 3rd BJT as follows: simulate this circuit On the left, I've included a current source. This is needed to provide the required recombination base current to drive one, the other, or likely both of the output drive NPN BJTs.

    Using a current source in this behavioral model is preferred because the required maximum recombination base current needed for the output BJTs is predictable from the design parameters. Since that maximum is predictable putting it under management is usually considered a "good idea. If you choose a different approach, you should be able to defend it well.

    The right side schematic is a rough equivalent to the left side and is what the rest of this answer will be based upon. As current sources are hard to come by, on the right I've done something called "bootstrapping.

    And a cheap one. There are equivalent methods for bootstrapping class-AB audio output stages. But those aren't discussed here. Driving the Output Stage We've got a behavioral concept for the class-A output stage, now.

    We need a comparator of some kind. It turns out that a single BJT can do this by comparing a signal at its base with a signal at its emitter. So a BJT can compare two signals. If, that is, variations in its collector current can be made useful. Here's how that might be made to work: simulate this circuit I've added a few boxes.

    One of them is a relatively simple AC divider. It divides down the output swing so that it can be compared with the input signal, Other than that, all we need to do is to supply the input signal and the magic happens. You may notice the arrows and some lettering I've added in red color.

    Let's see what happens if the voltage at A makes an undesired downward change. The downward change will be divided down by the AC divider-box, but will still be downward in direction when it appears at B. It also acts to establish the desired quiescent DC operating point, if everything is designed right. So don't be excessive. But there are several considerations here. Suffice it that it isn't critical. I'll leave detailed considerations for another time. I'll continue to expand the following discussion, as time permits.

    Beginning Topology The following will be based upon what I've already written up here. In particular, I'm selecting the class-A approach that is the main thrust at that link. The following ignores some of the development in the prior section.

    I'm not even going to waste time discussing them. See the link above, for more. Instead, I'll focus on the rest of it -- starting at the output side and working backwards, from right side towards left side. This is for educational purposes. It's not a professional design. I'm only a hobbyist. I don't get to do professional designs, by definition. Bridged, or otherwise, we need at least twice that at the speaker load. I'm not doing a bridged design. But to stay into class-A, it needs to be more.

    As a hobbyist, I can say this should provide enough margin. I happen to have some and a model of the D44H It's cheap. Here's a quick snapshot from its datasheet: I've circled the places where the minimum and maximum expected collector currents will be at. From this, it's clear the device has a fairly even response over the range we care about. Not perfect. But "good enough. I'm comfortable loosening up a bit on the current and using the slightly larger-than-computed value, instead.

    Those are the only options. Keep in mind this is a cheap, wasteful, class-A amplifier. In short -- a lot. You can work out the size from the lowest frequency you want to support. But for now, I'm just going to pick a large value that probably isn't large enough, but perhaps "adequate. Still conservative, as it is likely higher than that. I'm not going to go through the details of why, here.

    Just stick it in.

    Chapter 6 Transistor (BJT) Amplifiers – Electronic Circuit Analysis

    The quiescent current usage of the amplifier is in between 1 mA and 1. If the quiescent current drops beyond this particular limit it will likely be essential to tweak the value of R9. As is evident in the table, the amplifier functions efficiently with high impedance loudspeakers. Since speakers with impedances as large as ohms cannot be easily available, the choice is to try using a lesser impedance speaker having a complementing transformer.

    For instance an 8 ohm speaker may be employed with a transformer using a ratio of around Although the amplifier output power is not very high, it is however adequate enough when combined with a moderately efficient loudspeaker inside a silent area. The amplifier's voltage gain is around 50 and the 3 dB bandwidth is around Hz to 6 kHz. PCB Designs 1. It could be accustomed to amplify, and produce audible, impulses via oscillators functioning within the acoustic range, to track signals via a different audio amplifier that may be defective, to amplify some other signal to a acceptable power level for measuring or relay operation etc.

    In the modern times, one can find a lot of integrated circuit power amplifiers supplying outputs of 1 to 3 watts although the majority of them demand cautious layout of the circuit so that you can avoid instability an unstable amplifier might vibrate and become destroyed consequently.

    Furthermore, a discrete transistor amplifier is much more informative because voltages could be assessed to get a greater perception of its working.

    Hence the present small amplifier is developed applying discrete transistors that apart from being far more steady than IC based designs, is perfectly suited to the requirements of the user. Transistors Q2, Q4 and Q5 are cemented into a small aluminium that works as a heatsink.

    Simple Single Transistor Audio Amplifier Circuit

    How the Circuit Works This circuit is pretty typical of a great number of audio amplifiers. The primary voltage amplifier transistor Q3 runs the secondary match NPN plus PNP Q4 and Q5 that are buffers delivering large current gain yet lower than unity voltage gain. For the reason that bases of Q4 and Q5 tend to be appropriately two base emitter junctions aside, Q3 is employed to set the bias voltages for these BJTs. Transistor Q1 works like an error amplifier that analyzes the input voltage and a divided down variation of the output voltage.

    When there is virtually any variation it supplies a control voltage to Q3 so that the error is fixed. The dc bias point of the amplifier is additionally established by Q2 which is unaltered by R5 and this is separated through C3.

    To keep up a roughly constant current in Q3, capacitor C6 is positioned to ensure the voltage across R8 thus the current through it constant. Capacitors C4 and C5 are accustomed to offer frequency compensation.

    The input sensitivity of this small amplifier circuit is fine-tuned by adjusting the resistor R3 value.

    Audio Amplifier- A Brief Outlook to Its Many Types

    The circuit also features a low 2. Using a Small 5 Watt Amplifier The next small amplifier circuit can be used with any input audio signal coming from any suitable source such as from the cell phone headphone jack.

    Once connected and powered, the small 5 watt amplifier will be able to boost the output to a much amplified over any 8 ohm 5 watt loudspeakers. The 47K is used for adjusting the volume output of the amplifier, and the 22K preset is used for setting up the quiscent current of the amplifier. The 22k preset must be adjusted by connecting a small mA lamp in series with the supply line. And the input point A must shorted to ground.

    Next, adjust the 22k preset until there no illumination present on the lamp.

    Electronic – My BJT audio amplifier circuit isn’t working as expected

    The quiescent current of this amplifier is not set. The lamp could be removed now, and the amplifier used normally for the amplifying the input signal. The series coupling capacitors are so selected as to act as effective short circuits to AC signals, while they act as open circuit for DC biasing voltages. This is justified since the maximum reactance occurs at the lowest frequency and decreases with increasing frequency: Once it is an effective short circuit at lowest frequency of the signal to be amplified, it is more effective short circuit at all higher frequencies.

    To avoid notational ambiguity, the following quantities are defined below. Vbe is the varying voltage between the Base and the Emitter.

    Voltage across RL is the amplified output voltage. The waveforms are shown in Fig. Otherwise, the initial charging current of the capacitor may exceed the maximum rated current of the device and the device blows off. Use the Transistor always well under the maximum values of specifications. First we identify a Transistor device that provides voltage gain, power gain and efficiency and distortion characteristics according to the desired specifications of an Amplifier.

    Class of operation of Amplifiers to determine the circuit efficiency before fixing up the actual power input and power output conditions. Step 1 Selection of the type of a Transistor is the starting point of the design.

    Mini Audio Amplifier Circuits

    We change some devices and increase the supply voltage level. Which can increase the power for a speaker by about 4 to 6 watts. This circuit is quite ancient. It was also used as a booster circuit for cassette radio receivers.

    It has a frequency response of 44Hz to 33,Hz, can accept an input signal of up to 1 Vp-p, and is suitable for the power supplies of 18V to 22V. Then, see R1, R2 and R6 are voltage divider circuit.

    To bias the base pin of Q1. Thus, The base voltage of Q1 will be about half of the supply voltage. This is approximately equal to the output voltage as well. Because the D. This allows for maximum output signal swing without a hard clipping. The R7 and C9 are used to the decoupling in sound frequency range. Use D1 for biasing the pair of output transistors. To reduce crossover distortion.


    Audio amplifier circuit using bjt