Power amplifier circuit type

Regardless of whether it is a discrete component amplifier circuit or an integrated amplifier circuit, the final stage must be connected to the load, and to drive the load, the final stage of the amplifier circuit must output relatively large power. The amplifying circuit that can provide enough power to the load is called a power amplifying circuit, or power amplifier for short. In terms of energy control and conversion, there is no essential difference between the power amplifier circuit and other amplifier circuits, but the power amplifier does not simply pursue high output voltage or high output current, but pursues the output as much as possible under a certain power supply voltage. Possibly large power and efficiency. Different operating states of the amplifier have different characteristics, so in practice, different operating states should be selected according to different requirements of the power amplifier circuit.

1. Characteristics and application of power amplifier

Power amplifying circuits can be divided into Class A, Class B, Class A and B, and Class C according to the different conduction times of transistors.

1. Class A power amplifier

When the static operating point of the power amplifier tube is set in the middle of the load line, the power amplifier tube is in the conduction state during the entire period of the input signal, which is called a Class A working state, referred to as a Class A power amplifier. The advantage of Class A power amplifier is that the nonlinear distortion is small, but the disadvantage is that the static current is large, the tube consumption is large, the output power is small, and the efficiency is low. The theoretical maximum value of efficiency is 50%. Due to the small nonlinear distortion, Class A power amplifiers can be used in broadband power amplifiers. Due to low efficiency and low output power, Class A power amplifiers can be used in low-power amplifier circuits, and power synthesis technology can also be used to realize the joint work of multiple power amplifiers to obtain greater output power.

2. Class B power amplifier

When the static operating point of the power amplifier tube is set in the cut-off area, the power amplifier tube is only turned on when the signal is positive, and it is turned off when the signal is negative, that is, the power amplifier tube is only turned on within half a cycle of the input signal, which is called Class B Working state, referred to as Class B power amplifier. The advantages of Class B power amplifiers are small tube consumption and high efficiency. The theoretical maximum value of efficiency is 78.5%, and the efficiency in practical applications is about 50%. The disadvantage is that the output signal lacks half a cycle and the distortion is large. In order to compensate for this distortion and output a complete signal waveform, two complementary triodes are usually turned on in turn to form a complementary symmetrical power amplifier circuit. However, when the two triodes are turned on in turn, due to the existence of the dead zone voltage, when the input signal is lower than the dead zone voltage of the power amplifier tube, the tube is still in the cut-off state, so there is distortion at the intersection of the output waveforms of the two tubes. This is called "crossover" distortion.

3. Class A and B amplifiers

When the static operating point of the power amplifier tube is set at the lower part of the load line and close to the cut-off area, in the entire cycle of the input signal, the conduction time of the power amplifier tube is greater than half a cycle and less than one cycle, which is called Class A and B working conditions, referred to as A and B class power amplifier. In the Class B complementary power amplifier circuit, add proper bias to the bases of the two triodes, so that the two triodes are in the micro-conduction state when they are static, and when the two triodes are turned on in turn, the alternating process is relatively Smoothing, which reduces crossover distortion. The typical application of Class A and B power amplifiers is audio amplification output.

4. Class C power amplifier

In the entire cycle of the input signal, the conduction time of the power amplifier tube is less than half a cycle, which is called a Class C working state, referred to as a Class C power amplifier. In addition to the power amplifier tube, the Class C power amplifier also includes an output tuning circuit that functions as both a filter and an impedance matching function. At the same time, the base bias circuit and the collector bias circuit have special requirements. Class C power amplifiers are divided into three working states: undervoltage, critical and overvoltage due to different working conditions. When the triode works in the amplification region and the cut-off region, it is called an undervoltage state. When the triode just does not enter the saturation region, it is called a critical working state. When the triode enters the saturation region, it is called an overvoltage state. The waveforms of the collector output in the three states are sharp cosine pulse, slightly flat cosine pulse and top concave cosine pulse respectively. The Class-C amplifier and the resonant circuit together constitute a Class-C resonant power amplifier or a Class-C frequency multiplier. Class C power amplifiers work in overvoltage and critical states with high efficiency, which can reach 100% in theory, and the actual efficiency is about 70%.

2. Typical power amplifier circuit and its application

According to different output coupling methods, the power amplifier circuit is divided into transformer coupling power amplifier circuit, no output transformer (OTL) power amplifier circuit, no output coupling capacitor (OCL) power amplifier circuit and bidirectional push-pull no output transformer (BTL) power amplifier circuit. amplifier circuit, etc. In addition, power amplifying circuits can also be divided into discrete component power amplifying circuits and integrated power amplifying circuits.

With the development of electronic technology, integrated circuits have become the core devices in modern electronic circuits and are widely used in various electronic devices. LM386 is an audio integrated power amplifier circuit, which has the advantages of wide frequency response, low power consumption, adjustable voltage gain, wide applicable power supply voltage range, few external components and small total harmonic distortion. It is widely used in tape recorders, radios and on the intercom.

With the further study of the amplifier circuit, its classification is more and more, and its application is more and more extensive. Only by mastering the various states of the amplifying circuit can it be flexibly applied as needed.

The above are the characteristics and applications of the power amplifier circuit introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have software and hardware function development needs for smart electronic products, you can rest assured to entrust them to us. We have rich experience in customized development of electronic products, and can evaluate the development cycle and IC price as soon as possible, and can also calculate PCBA quotations. We are a number of chip agents at home and abroad, including MCU, voice IC, Bluetooth IC and modules, wifi modules. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth wifi development, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS solutions, the development of Bluetooth audio, the development of children's toys, and the development of electronic education products.