Last Updated on October 22, 2023 by Kevin Chen
Image source Freepik
Audi amplification is among the most common applications of transistors. These amplifiers are designed to level up the audio signals. An increase can be in terms of the power and frequency of the signals. Audio amplifiers are connected to different audio signal sources such as microphones, mouthpieces, musical instruments such as guitars, and many other devices. The amplifiers take these signals as input and are supposed to release them to the audio output devices such as speakers and headphones. In all these circuits, the main function of the audio amplifiers is to boost the signals. It is through the audio amplification that the roles of transistors come out clearly.
Both the Field Effect Transistor (FET) and bipolar junction transistors (BJT) transistors are used in audio amplifiers. They are installed at different ends of audio processing devices. Some are installed at the transmitters while others at the receivers.
Transistor as an amplifier
As an amplifier, a transistor is designed to boost the strength of the weak input signal. Hen included in an electric circuit, the DC voltage is connected to the emitter-base junction of the transistor. The transistor will remain in a forward-bias mode as illustrated in the simple electric circuit below.
Image source Tutorialspoint
In the image above of a simple electric circuit, the input circuit has a small resistor. A change on the input signal, no matter how small it may be, will have a direct change on the output signal. The electric current that is flowing through the emitter is due to the input signal. This current will constitute the collector current and will flow through the load resistor leading to a voltage drop (Rl). A small input voltage will result in a higher output voltage, meaning that the transistor acted as an amplifier.
Transistors as amplifiers must operate at the active region (the other two regions are saturation and cut-off regions) They are able to achieve a power gain on the circuit without the requirement of help from the external power sources.
The BJT transistors for amplifiers are installed in different configurations. These are the common base, common collector, and common emitter configurations.
Functions of transistors in amplifiers
Here are the key roles of transistors in audio amplifiers
This is the primary role of transistors in audio amplifiers. Both the BJT and FET transistors are designed to boost the incoming signals in audio amplifiers. In most cases, the incoming signals are weak in terms of power and quality.
The transistor will increase the power of the audio circuit resulting in powerful and high-quality output signals. The amplification of the audio signal is usually proportional to the input signal as well as the power capacity of the transistor.
They are used as switches
Other than amplification, switching is another important role of transistors in audio amplifiers. Transistors are designed to operate like other electric circuits, they can be turned ON and OFF.
By including a transistor in an audio amplifier, it becomes easy to switch the device between two states. You can easily determine when the signals should flow all the way to the output audio devices or not.
The fast-switching speed of transistors is among the top reasons why they are used as switches in audio amplifiers. A perfect example is the class D amplifier which is used in small devices. Transistors make it easy to use these amplifiers.
Regulation and stabilization
The fact that transistors are directly connected to the incoming circuits means that they can play a role in regulating the input voltage of the audio amplifiers. One of the ways in which this is achieved is through biasing the transistors.
A biased transistor will always operate in its active region. It will also ensure that the input signal meets the minimum requirements hence ensuring that the output signal is clear and smooth.
Signal matching is another way in which transistors stabilize the signals in audio amplifiers. They ensure that the output signals are proportional to the input signals.
Classes of audio amplifiers
Additionally, there are different classes of audio amplifiers in which the transistors are used. The amplifier classes are based on the applied input as well as the output from the circuit. These classes include the following:
- Class A amplifiers: This class of amplifiers comprises of a single transistor that performs the whole amplification role. Compared to other classes, this one has low-efficiency levels.
- Class AB amplifiers: Here, there are two active electronic components that conduct the audio signals. One transistor conducts the positive signal while the other component is in charge of the negative signal.
- Class D signals: This class of amplifiers drives their amplification performance using pulse-width modulation technology (PWM). The incoming signals into the circuit are first converted into digital pulses before being channeled to the transistors for amplification. This class of amplifiers is quite common in most portable and small audio devices.
Other than the classes, transistors also help to achieve different stages of amplification on the audio amplifiers. These classes include preamplification and power amplification. Preamplification entails preparing the signals for the actual power and voltage amplification. Power amplification boosts the signal strength as it heads to the speaker or any other audio output device
Now you know how a transistor works as an amplifier and the roles that it plays in audio amplifiers. If you are working on a project that entails building audio amplifiers, transistors should be among the essential electronic components that you should get.
One clear thing is that for a transistor to be used for audio amplification, it should be highly efficient to achieve the gain linearity in amplifiers. This happens when a change on the input signals is proportional to the output signals. To achieve this, you should pay special attention to the technical specifications and parameters of the transistor. The parameters should match those of the circuit.
Once you are sure of the parameters, you can proceed to contact reputable transistor suppliers in China to place your order. Of course, this should happen after you are sure of all the other fine details of the transistor.
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