Many people may not be fully aware of the classifications of audio power amplifier ICs, their characteristics, or the common types available. Here, I will explain these concepts in detail. Common audio power amplifier ICs can be broadly classified into nine categories:
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Class A Amplifier (Also known as A-Class Amplifier): Class A amplifiers are those in which all power output elements remain conducting throughout the entire signal cycle (both positive and negative halves of a sine wave). The major drawback of Class A amplifiers is their low efficiency, as full current flows even when there is no signal, converting all electrical energy into heat. As signal levels increase, some power is delivered to the load, but much still turns into heat.
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Class B Amplifier (Also known as B-Class Amplifier): Class B amplifiers use a push-pull output stage where the two “arms” alternately amplify the positive and negative halves of a sine wave. Each “arm” conducts for half of the signal cycle.
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Class AB Amplifier (Also known as AB-Class Amplifier): Class AB amplifiers fall between Class A and Class B. Each “arm” of the push-pull amplification conducts for more than half but less than the full signal cycle. A notable characteristic is severe distortion at very low signal levels due to crossover distortion, making the sound rough. Class B amplifiers have an average efficiency of about 75%, producing less heat than Class A and allowing for smaller heatsinks.
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Class C Amplifier: Class C amplifiers are less commonly heard of because they are highly distorted and suitable only for communication applications. They have extremely high output efficiency but are not suitable for HI-FI amplification.
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Class D Amplifier (Also known as D-Class Amplifier or Digital Amplifier): Class D amplifiers work on the principle of switching transistors, which can be fully on or fully off in extremely short periods. Since no two transistors are on at the same time, heat production is minimal. The advantages of Class D amplification include maximum efficiency, allowing for smaller power supplies, little heat generation, and thus no need for large heatsinks. The amplifier body is significantly reduced in size and weight, with theoretically low distortion and excellent linearity. However, their complexity and the inherent deviations in added circuitry mean that truly successful products are rare, and they are not cheap.
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Class E Amplifier: Class E amplifiers are high-efficiency switching amplifiers. Additionally, polar transmitters based on Class E amplifiers can improve the low efficiency of traditional transmitters.
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Class F Amplifier: Class F RF amplifiers are a new type of high-efficiency amplifiers with a theoretical efficiency of up to 100%. They have broad development prospects in the field of mobile communications. Class F amplifiers achieve efficiency and output power enhancement by forming drain waveforms in the output matching network using harmonic oscillation circuits, with even harmonics shorted and odd harmonics open at the load.
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Class K Amplifier: Class K amplifiers are integrated forms that combine bootstrapping and power amplification. This type of amplifier can be varied, such as Class D or Class AB, depending on the need.
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Class H Amplifier: Class H amplifiers are special application types where the power supply can maintain high voltage following output changes. They are commonly used in automobiles. However, since the advent of Class D amplifiers, Class H amplifiers have become less common.