Different from professional power amplifiers, the design requirements for simple audio amplifiers are not complicated. However, matching transistors are still needed to ensure their performance and reliability. When selecting transistors, the following aspects need to be considered:
Sufficient Power Capacity
The capacity of a transistor is one of the important parameters.It is necessary to choose transistors with sufficient power capacity to withstand the peak output power of small amplifier. Normally, the power capacity should be 2-3 times the peak output power. For example, if the peak output power is 50W, the transistor should be at least 100W to withstand the voltage and current at peak output.
Voltage and Current Capacity
The voltage and current capacity are also key factors in selecting a suitable transistor. It should be able to withstand the working voltage and current of the peak power. Generally, the voltage and current capacity of a transistor should be 2-3 times of the power amplifier. For example, if the working voltage is 200 V and the rated output power is 50 W, the voltage capacity of the transistor should be at least 600 V. Besides,the current capacity should be at least 10 A.
The operating frequency of the transistor needs to match the operating frequency of the power amplifier. Transistors with different operating frequencies have different electrical properties and packaging forms, so it is necessary to choose the appropriate transistor based on the operating frequency of amplifier. For high-frequency power amplifiers, it is necessary to choose high-frequency transistors; For low-frequency simple amplifiers, universal transistors can be used.
Gain and Noise Coefficient
The gain and noise figure of transistors also have an impact on the performance of amplifiers. Normally, the gain should be 2-3 times that of the amplifier, and the noise figure should be lower than the noise figure of the amplifier. For example, if the gain of the PA AMP is 20 dB, the transistor should be at least 40 dB accordingly, and the noise figure should be less than or equal to the noise figure of the PA AMP.
Packaging Form and Heat Dissipation Capacity
The packaging form and heat dissipation capacity of transistors have an impact on the reliability of amplifier. Different packaging forms have different heat dissipation and electrical performance, so it is necessary to choose the appropriate packaging form based on the needs and usage environment of the audio amplifier.
General Design Requirement
In summary, selecting the right transistor requires consideration of a number of aspects, including power capacity, voltage and current capacity, operating frequency, gain and noise factor, as well as package form and heat dissipation capability. The appropriate transistor needs to be selected according to the specific needs of the amplifier and the environment in which it will be used. Factors such as cost and availability of transistors also need to be considered. Comprehensive considerations need to be made when selecting transistors to achieve optimum performance and reliability.
In addition, apart from choosing the right transistors, other factors such as circuit design, power supply stability, heat dissipation design, etc. need to be considered. Therefore, when designing and selecting audio amplifiers, several factors need to be considered comprehensively to ensure their performance and reliability.