Abs amplifier
The extruded aluminum heatsink provides high efficiency thermal performance; using the top side of the heatsink to effectively dissipate the heat generated by the electronic components. The internal temperature remains constant at all power levels. Filtered pre-amplified outputs along with multiple adjustments are featured on the HCP 1D, offering the user endless connection possibilities with any source. Special balanced input circuitry rejects electro-magnetic disturbances present on the Pre-amplified or Speaker level inputs. This function can also be disabled. Where to buy Find a distributor.
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Class AB Amplifier
We learned that the conduction angle of a Class A amplifier is degrees, meaning that the amplifying element is conducting current throughout the entire cycle of a sine wave that is being amplified.
We saw that Class A amplifiers offer reasonable linearity, but have poor performance with respect to efficiency. We are now going to look at push-pull Class B and Class AB amplifiers, which are comprised of devices with conduction angles less than degrees.
These amplifiers can be made to be more efficient than Class A amplifiers, but suffer from a particularly undesirable form of distortion known as crossover distortion.
We will investigate crossover distortion and some commonly-used methods to ameliorate it as we progress through the lab. An ideal Class B amplifier has a conduction angle of degrees, or one half-cycle of a sine wave. This type of amplifier therefore requires two amplifying elements to produce a full sine wave at its output.
One of the elements conducts for the positive portion of the signal being amplified and the other conducts for the negative portion of the signal. For a sine wave, the positive portion of the signal is the positive degree half-cycle of the waveform and the negative portion of the signal is the negative degree half-cycle of the waveform. This is where the definition of the degree conduction angle originates.
An amplifier that uses two amplifying elements in this type of arrangement is often referred to as a push-pull Class B amplifier because one device pushes current into the load and the other pulls current from the load. V BE characteristics. If we are designing the positive half-cycle section of a complementary push-pull Class B amplifier with a NPN BJT, we could connect the emitter to ground and drive the base directly. In this case the input voltage would have to rise to at least 0.
When the input was substantially less than this, the transistor would be off and no significant emitter or collector current would flow. It is not completely correct to describe this type of amplifier as Class B, therefore, since no current flows in the devices in their dead zones, and this situation produces a conduction angle of less than degrees. This undesirable type of distortion happens when the sine wave is crossing over from positive to negative, or negative to positive, and is appropriately called crossover distortion.
Crossover distortion in a BJT-based push-pull Class B amplifier is generally unacceptable because it is so large, so we need to find ways to minimize it. The most common way is to provide a small amount of bias to each transistor such that they are just barely on when the signal crosses over from negative to positive or positive to negative.
If we were to bias each transistor such that it is perfectly on the verge of conducting with no input signal applied, we would have something as close to a perfect push-pull Class B amplifier as we could achieve since the conduction angle for each device would be very close to degrees. In other words, an extremely small input voltage would cause one of the transistors to go from the non-conducting state to the conducting state.
Real transistors do not have a perfectly abrupt transition between non-conducting and conducting states, however, so we cannot achieve perfect Class B operation even with the bias added. The best solution is to bias each transistor such that it is conducting a small amount with no input signal applied. Because we are adding a small amount of bias in addition to what is required to overcome the base-emitter drop, the resulting amplifier is called a Class AB amplifier because it has a small amount of Class A bias in it to reduce the crossover distortion.
We can lower the crossover distortion if we bias the input voltage up at least 0. By doing this to each section we can cancel out most of the ill effects incurred due to the V BE voltage drop. This can be accomplished are by using another transistor or diode to provide the V BE voltage drop, using a resistive voltage divider not usually done for reasons we will see later , or some other equivalent means.
Diodes and transistors that are used to shift the DC levels of signals are called level shifters. Class AB amplifiers are often used as amplifier output stages in emitter-follower and common-emitter configurations. The common-emitter Class AB stage is used in rail-to-rail operational amplifier op-amp stages in order to allow the output voltage to swing very close to the power supply voltages.
In this lab we will first build a push-pull class B common-emitter amplifier comprised of one NPN and one PNP transistor and use this to illustrate the large crossover distortion that is produced without transistor biasing.
We then add biasing and observe how doing this significantly reduces the crossover distortion. Providing a thermally stable, well-positioned bias point can be the most challenging part of a Class AB amplifier design. To study and understand push-pull Class B amplifiers constructed with BJTs as the amplifying elements and view the characteristic crossover distortion associated with them.
To see how using level shifters to add a small amount of bias to the Class B amplifier sections to produce a push-pull Class AB amplifier can significantly reduce crossover distortion. To understand how the crossover distortion mechanism differs from other distortion mechanisms, and gets worse as a percentage of signal amplitude as the output signal gets smaller. To understand how thermal runaway can occur in Class AB amplifiers and investigate techniques to prevent it.
Following completion of this lab you should be able to explain the basic operation of push-pull Class B and Class AB amplifiers that use BJTs as the amplifying elements, describe crossover distortion, explain how and why it happens, and how it differs from distortion caused by other mechanisms, describe what level shifters do, and explain what can cause thermal runaway in Class AB amplifiers, why it can be dangerous, and how it can be prevented.
The clear solution to this problem was to add just enough DC bias voltage such that each transistor is slightly conducting collector current with no signal applied to the amplifier input. This solution works quite well, but has a few drawbacks, one of which is the potential for thermal runaway. Thermal runaway is a form of positive feedback, sometimes referred to as a self-reinforcing feedback loop, in which a change in a system operating condition pushes the system away from a desired stable point instead of toward a stable point.
Stable systems are designed using negative feedback in which changes in the system operating conditions push the system back toward its desired stable state. A simple example of a naturally-occurring negative feedback system is the system that regulates the amount of light that enters the eye by controlling the diameter of the iris diaphragm.
When the light entering the eye increases beyond the ideal amount, the iris diaphragm decreases in diameter until the light reaches its ideal level. Similarly, when the light entering the eye decreases below the ideal level, the iris diaphragm increases until the light reaches its ideal level.
Thus, negative feedback drives the system to decrease the error between an ideal condition and the actual condition. Positive feedback systems do just the opposite of negative feedback systems. A simple example of thermal runaway is what can can occur in carbon composition resistors that have negative temperature coefficients NTC , that is, the resistances of these resistors decrease with temperature.
As a NTC resistor heats up its resistance decreases, causing it to draw more current, which further decreases its resistance, causing it to draw even more current, and so on. If not limited by something, this process can continue until the resistor overheats and destroys itself.
The worst bias arrangements for Class AB amplifiers with respect to thermal runaway are those that use bias voltages that are relatively fixed over temperature.
A resistive voltage divider network provides bias voltages that are relatively fixed with temperature, and this is why they are not widely used as Class AB amplifier bias circuits.
The following schematic illustrates a simple resistive voltage divider bias circuit that could be used to bias a BJT-based Class AB amplifier. A potentiometer could also be placed between the two bases with a slightly different arrangement to provide an adjustable bias. In the schematic above the input signal would be applied between R B2 and R B3.
When properly designed, the voltage between the two bases would be equal to 2V BE on where V BE on is defined as the base-emitter voltage at which each transistor begins to conduct.
The thermal runaway problem with fixed bias can now be addressed. The collector current and base-emitter voltage have an exponential relationship, which must be obeyed. Since the base-emitter voltages are not allowed to decrease due to the fixed bias voltages provided by the voltage divider, the collector current increases instead according to the exponential dependence of I C on V BE.
This arrangement presents an exponential dependence of collector current on temperature. As the collector current increases the base-emitter junction temperature increases, further increasing the collector current.
Much as was the case in the carbon composition resistor, we have an unstable self-reinforcing feedback loop in the amplifier which produces thermal runaway, and will eventually destroy the transistors. Fortunately, there are a number of better biasing schemes that can be used to avoid thermal runaway. If we replace R B2 and R B3 with forward biased diodes, or transistors configured as diodes, we can cancel out the effects of the negative V BE temperature to a great degree as long as the current vs.
This is what we did in the lab when we added the transistors connected as diodes to the Class B amplifier to change it to a Class AB amplifier. A further improvement can be made to the circuit by converting the transistors connected as diodes to emitter follower stages, providing a high input impedance to the amplifier. This type of arrangement is commonly called a diamond stage.
Sometimes, however, this thermal compensation may not be enough to entirely avoid thermal runaway, since devices are not perfectly matched, and temperatures can vary between devices. A heat sink, if available, can be used to help equalize the temperature among all of the devices if all of the devices are thermally connected to it. Another technique that is often used is to place small resistors in series with the emitters of the amplifier transistors.
This is why we placed the two 1. Crossover distortion is worse than other types of distortion since it is not reduced as a percentage of signal amplitude as the signal amplitude is reduced. Other distortion mechanisms produce harmonic distortion distortion of the shape of a sine wave from its ideal shape that scale with amplitude over a wide dynamic range, giving a rather constant percentage of harmonic distortion as the signal amplitude is varied.
Crossover distortion, on the other hand, does not decrease with signal amplitude -- the dead zones stay the same -- so the distortion percentage in a signal actually increases as its amplitude decreases. Fortunately, negative feedback is often provided around amplifiers with push-pull Class AB output stages, which significantly reduces signal distortions.
Clearly, the amplifiers themselves should be designed to produce minimal crossover distortion without the negative feedback. Return to Engineering Discovery Index.
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This version 03 Jan was approved by Doug Mercer. The Previously approved version 05 Dec is available. Data sheet handout for the 2N NPN transistor. Construct the following circuit on the solderless breadboard. Refer to the illustration below for one way to install the components in the solderless breadboard.
Observe the output voltage at the connection between the two emitters on Channel B and observe the large amount of crossover distortion that is present in the output signal as shown in the image below. Observe the output voltage at the connection between the two emitters on Channel B and observe how the crossover distortion has been significantly improved due to the addition of the level shifting transistors, connected as diodes.
Estimate the voltage loss factor due to the voltage divider formed between the amplifier output resistance and the load resistance. Increase the input voltage amplitude to swing between 0. Ideal Class B amplifiers have conduction angles of degrees.
A/B Amplifier
The professional-grade Devine MA amplifier delivers two-time Watts at 4 Ohms or Watts at 8 Ohms when set up in bridge mode. Built to provide the core of a pounding PA system, this class-AB amplifier can drive a pair of full-range satellites while backed up by automatic signal peak protection, short-circuit protection, and overdrive protection. Since this amp is fairly weighty, it comes fitted with two extra rear rackmounts for secure installation, while integrated vents protected by anti-dust material keeps the unit cool while keeping dust out. Fitted with jack as well as XLR inputs, a pair of locking speaker outputs, and a third central locking speaker output for bridge mode, the hard-working Devine MA amplifier guarantees a professional performance.
A Reconfigurable Class-AB/F Power Amplifier for 0.1–4.2 GHz Multistandard Applications
The only commonality between them is the name. Amplifiers work by converting the incoming DC voltage into AC power through the transformer. Some are more efficient than others, and some provide more fidelity than others. The upgrade aimed to solve the problems in both classes. Class AB amps are now the most used amplifier class in home theaters and stereos. Instead of the distortion issues of Class B amplifiers, Class AB amps allow both devices to conduct simultaneously. A Class D amp is actually an analog device. The reason is simpler than you think. It was the next letter in the alphabet after Class C. Each class works differently than the other.
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In this tutorial, i will try to explain how to make an amplifier circuit known as Class AB Amplifier. There are a lot of amplifier circuits and have their circuit analysis methods as well. However, i will cover the only basic implementation of it with the two stages. First stage consist of non-inverting amplifier circuit using Op-Amp. It is for the amplicitaion of small signal araound more than 20 times.
MA-LM02 Stereo Amplifier board LM3886T Class AB 2x 68W
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Class-AB Audio Power Amplifiers
Outstanding expertise in amplifier development. They can be used to address a variety of applications, including the various standards for EMS measurements up to 6 GHz. Other fields of use include research, physical engineering and communications. The compact and modular design allows single band or multi band configurations in 4HU desktops or in 19" racks for high power. They can be flexibly scaled and upgraded in terms of frequency and power. It secures customers' investments and offers them the flexibility to adapt their systems to new requirements at a later point in time. They are rugged enough to handle short-circuiting at the RF end or an open RF output.
Automotive Class-AB Audio Power Amplifiers
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S09 Siren Amplifier
RELATED VIDEO: Cheap Chinese (BT-309A) Power Amplifier Unboxing, Review, and Teardown.Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. This is a beginner's theoretical question. What I don't understand is that the output signal is coming from two transistors, additive.
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Amplifier Design Concepts Includes: Basic concepts Amplifier classes Amplifiers are given a classification according to the way in which they are biassed and they operate. The class of an amplifier is selected to meet the overall requirements. Different amplifier classes provide different characteristics, enabling the amplifier to perform in a particular way and also with a level of efficiency. The different amplifier classes provide different performance characteristics.
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