Class ab amplifiers can be biased by choosing an operating point along this blue line, excluding the class a and class b biasing points. As might be expected a class ab amplifier falls between class a and class b. The tda8953 is a stereo or mono high efficiency class d audio power amplifier in a single ic featuring low power dissipation. The only disadvantage of class a power amplifier is the low output power and low collector efficiency. Values below 1ma are common in op amp ics, whereas high power audio amps may have values up to 100ma or more. Majority of the power wasted is lost as heat on the active elements transistor. The limitations due to the efficiency of class a power amplifiers.
If the class ab operating point is closer to the class a operating point resp. Design and compensation of high performance class ab. Class b stage the efficiency of a power amplifier may be increased using the following fig. Class ab amplifiers are a combination of class a and class b amplifiers. We have seen that the power output of an amplifier is the product of the. Class a, class ab, etc specify output voltage in terms of fundamental and harmonics of voltage. Amplifier classes and the classification of amplifiers. It embeds 4 audio channels able to deliver a maximum power of 50 w each, it can drive loads as low as 2 w and operate from 6 to 18 v without popping or interruption. This is the whole reason for the invention of class d amplifiers. Vgg3 and vgg4 can be used to bias this amplifier in class ab or class b operation. Power conversion efficiency similar to class b disadvantages. Pdf a procedure for analyzing, designing, and assessing audio power amplifier output stages operating in classes a, b, ab, g, and h with. Efficiency of a class ab amplifier all about circuits. Class a amplifier design produces a good linear amplifier, but most of the power produced by the amplifier goes wastage in the form of heat.
The maximum efficiency is reached if and and under these conditions, the efficiency becomes. The class ab circuit, over most of its input signal range, operates as if the q n or q p transistor is conducting and the q p or q n transistor is cut off. The function of a practical power amplifier is to amplify a weak signal until sufficient power is achieved to operate a loudspeaker or output device. Class ab is typically 60% efficient with 40% of power. There are a lot of class d amplifiers available as smsl sa50 tda7492, fosi audio class d amplifiers, power acoustik 4 channel class d amplifier, class d audio power amplifiers, sure electronics tda7492 class d audio amplifiers etc. Class ab and class c power amplifiers tutorialspoint. Class a power amplifier theory, efficiency equation. Class a, class b, class ab and class c amplifier scary. The output amplitude is a nonlinear function of the input, so class c amplifiers are not used for. Somewhat like a class g or h amp, the class b amp sustains the output most of the time, but the class c amp cuts in on high signal peaks. As a result, even a moderately powered class a power amplifier require a large power supply and a large heatsink. By contrast, linear ab class amplifiers are always operated with both current flowing through and voltage standing across the power devices. The benefit of the doherty is increased efficiency.
Provide sufficient output power in the form of voltage or current. This is done by adding two emitter resistors and three diodes or diodeconfigured transistors to force a voltage difference between the bases of the transistors. The above expression shows that in class a amplifier, maximum 50% of the dc power supplied can be converted into ac power output. A linear rf power amplifier with high efficiency for. Pe is the power conversion efficiency reflecting the percentage of the dc power drawn from the power supply, which has been converted into. Using this approximation we see that a class ab amplifier acts much like a class b amplifier. Realworld power mosfets are not ideal switches, but practical efficiencies well over 90% are common. Class c amplifiers are biased so that conduction occurs for much less than class c amplifiers are more efficient than either class a or pushpull class b and class ab, which means that more output power can be obtained from class c operation. The diyaudio diyab class ab power amplifier or honey badger as we call it at diyaudio hq was designed to fill the needs of members that require a high power amplifier with similar capabilities and characteristics to those found most in modern, expensive high end commercial amplifiers. Due to power loss in the primary of the transformer, the collector efficiency of class a amplifier is always less than 50%. In doing so, we will not consider the small power consumed in the basebiasing circuit, i.
Next, the pa design problem from a unified, general point of view based on the internal pa. It may be noted that maximum power is dissipated in the transistor in the zero signal. Class j has been implemented using gan fet in high power applications. Complementary symmetry class b and class ab power amplifiers the circuit for a typical pushpull power amplifier is shown to the right figure 8. What is the difference between class ab, and class d. However it suffers from poor efficiency, because to bias the transistor in the. Although seldom used in high power amplifier applications due to thermal power. The class a amplifier has great fidelity, it stays true to the original signal. Class ab sacrifices some efficiency over class b in favor of linearity, thus is less efficient below 78.
Power dissipation for low signal levels higher than class b. An ideal class b amplifier has a theoretical maximum efficiency of 78%. Class d wastes less power limiting the need of heat sinks. So, the class ab is a good compromise between class a and class b in terms of efficiency and linearity having the efficiency reaching about 50% to 60%. The class ab amplifier is a blend of class a and class b, and strives to offer a compromise in efficiency and performance. The classes are based on the proportion of each input cycle conduction angle during which an amplifying device passes current. The image of the conduction angle derives from amplifying a sinusoidal signal. What are amplifier classes and their power efficiencies. Class ab power amplifiers are slightly inefficient than the class b configurations but far better in terms of distortion when compared to class a configurations. Class ab arrangements are probably the most commonly employed system for power amplifier output sections, although pure class a is often used for low currentvoltage applications where the poor power efficiency isnt a problem. The reduced conduction angle progresses the efficiency to a. Pdf on the design and efficiency of class a, b, ab, g, and h audio. If the collector current flows only during the positive halfcycle of the input signal, it is called as class b power amplifier.
Electronics tutorial about the class ab amplifier circuit that is forward biased to eliminate. It has smaller heat dissipation, so small heatsink is needed. Its quiescent power consumption is comparable with a class ab amplifier. Since the active devices are slightly prebiased there will be a small amount of collector current flowing and this is the reason behind the slightly reduced efficiency. The circuit requires various switching components like mosfets which has low on resistance. The choice of its location depends on the desired levels of efficiency and linearity. This class of amplifiers are designed to reduce the less efficiency problem of class a amplifiers and distortion of signal at crossover region in class b amplifiers. The class a, b and ab amplifiers are called as linear amplifiers because the output signal amplitude and phase are linearly related to the input signal amplitude and phase. The linear amplifiers is inherently very linear in terms of its performance, but it is also very inefficient at about 50% typically for a class ab amplifier, whereas a class d amplifier is much more efficient, with values in the order of. Though the efficiency of class b power amplifier is higher than class a, as only one half cycle of the input is used, the distortion is high. It depends on the voltage out as to how much is power to the speaker and how much to the heatsink. Class c operation, especially for high efficiency, high power radio frequency rf amplifier applications. The main objective of this project was to design a 100w power amplifier with feedbackpair complementary symmetry output power transistors.
Know all about classc power amplifier circuit and tutorial. The class ab pushpull output circuit is slightly less efficient than class b because it uses a. The advantage of class d is its high efficiency 8090% because the output transistors are either turned fully on or fully off during operation. It maintains high frequency response like in class a amplifiers and good. Power amplifiers purpose of a power amplifier generate high output power efficient conversion of dc power to rf power linear amplification generally pas will be common source cascode inductor is a choke to provide d apacitor is a ac coupling path to output james buckwalter 2. Amplifiers on this class are suitable for a wide range of highend audio applications. The class ab pushpull output circuit is slightly less efficient than class b because it uses a small quiescent current flowing, to bias. Class a amplifier circuit operation and applications. Class d amplifier is the highest power efficient amplifier class in the a, b, ab, and c and d segment. In this topology, each of the pair of complementary active elements is biased slightly into the active region, and so there is some overlap between the two at the turnonturnoff center point, figure 3. Power amplifier circuits output stages are classified as a, b, ab and c for analog designsand class d and e for switching designs. In order to compensate these problems, the pushpull configuration is introduced in class b amplifier. This means 75% of power drawn by the amplifier from the supply line is wasted.
The class ab amplifier cores presented here improve the amplifier s power supply noise insensitivity at high frequencies and increase bandwidth efficiency when compared to the commonly used twostage miller compensated amplifier, enabling the construction of better buffers and more power efficient and reliable low voltage mixed signal chips. The stpa008 is the latest automotivegrade class ab analog input power amplifier of the stpa family designed to enrich the car audio listening experience. Overdriven amplifiers for very large input signals, the output waveform. Pout is the amplifiers output power delivered to the load pdc is the dc power taken from the supply for a power amplifier it is very important that the amplifiers power supply is well designed to provide the maximum available continuous power to the output signal. These are just a few examples, there are a lot more of this class amplifiers. Power amplifier waveforms inspired by steve cripps rev 1. The diode biasing circuit, as we just presented before, is the most adapted to bias class ab amplifiers. Ece 3274 power amplifier project push pull qty device. It is a widely used topology in digital audio players or controlling the motors as well. Class d efficiency is typically in excess of 95% compared with 60% for a class ab amplifiers.
Since the transistors in class a amplifier, are forward biased all the time, few current will flow through them even though there is no input signal and this is the main reason for its poor efficiency. Can be efficient if operated in class b or class ab lecture 060 pushpull output stages 11104 page 06010. The schematic diagram of a practical power amplifier is shown below 2 the driver stage operates as a class a power. Design and construction of class ab audio amplifier. Understanding amplifier operating classes electronic.
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