Power Amplifier
Amplifier is an electronic device or circuit that is used for increasing the power of the (weak) output signal. These amplifiers are classified into various types such as voltage, current, power, linear, non-linear, transresistance, transconductance, and so on. In fact, amplifiers are different types which are specially used for some specific applications. Here in this article let us discuss about power amplifier working in a FM, but, primarily we must know what is a power amplifier.
What is a Power Amplifier?
The power amplifiers which are classified into various types based on applications such as audio power amplifier, radio frequency, fm amplifier (power amplifier used in fm), transistor, stereo power amplifier, valve power or vacuum tube power amplifiers, class A, class B, class C, class D, class AB power amplifiers, etc.,. These power amplifiers are used for amplifying the output signals with weak input signals. These specific power amplifiers are specially used various specific applications. In this article, let us consider fm amplifier, stereo power amplifier, and how does a power amplifier work.
How does a Power Amplifier Work?
There are different designs in power amplifiers with different ratings such as 50W, 20W, and 10W RMS values. But, practically the power amplifier must be capable of driving the desired load. Practical audio power amplifier circuit consists of specific circuits to produce voltage and current gains. The practical power amplifier circuit consists of different stages such as a voltage amplification stage, driver stage, and output stage as shown in the block diagram below.
Power Amplifier Stages
Voltage Amplifying Stage
In general, the input signal given to the electronic amplifier from the source is not strong enough (it is very weak and is in the range of millivolts) to drive the successive stages. Thus, in this stage primarily the voltage amplified such that it is made to strong enough process the successive stages. This purpose can be fulfilled by the class A amplifiers and required voltage gain can be achieved by using two or more RC coupled class A amplifiers.
Driver Stage
This stage can be considered as an intermediate stage, which stands between the voltage amplification and output stages. The first stage alone is not enough to drive the output stage as it is having a low input impedance. Thus, this driver stage acts as an intermediate stage that can generate the current gain and sufficient power gain too.
Output Stage
This stage is connected to the output (loudspeaker), this stage improves power gain further and supplies to the output with very least power loss. There are two configurations for the output stage, single transistor or push-pull arrangement (two active devices, transistors). But, push-pull arrangement is mostly preferred compared to single transistor as it is having advantages such as high power output, efficiency, even-harmonics cancellation, DC current cancellation, and so on.
Practical Power Amplifier Circuit
The practical circuit diagram for the power amplifier circuit is shown in the figure below.
Power Amplifier Circuit
The power amplifier circuit consists of three stages such as voltage amplification, driver, and output stages which we discussed earlier in this article. The voltage amplification stage can be formed using Q1, signal transistor and basic electronic components as shown in the circuit. The transistor Q1 is biased using resistors R1 & R2, the DC components can be blocked from the input signal using coupling capacitor C4 at the input. The current passing the biasing network can be limited using resistor R7 and C1 is used as a filter capacitor. The transistor Q1 collector terminal provides the output of the voltage amplification stage.
The driver stage is formed by Q2, power transistor and the base terminal of this transistor is directly coupled to the voltage amplification stage output. The transistor Q2 collector terminal provides driver stage output.
The output stage can be formed using the power transistors Q3 & Q4, which are wired in the push-pull arrangement. The transistors Q2 (collector terminal) & Q3 (base terminal) and transistors Q2 (emitter) & Q4 (base) are connected as shown in the circuit. The circuit output is drawn from the emitter-base junction of the output. The output transistors emitter-base junction provides the entire circuit output.
There are various amplifier circuits such as stereo power amplifier, earphone amplifier circuit, Hifi audio amplifier circuit, and so on. If you want to design amplifier based electronics projects on your own, then you can download our free eBook to design do it yourself projects.
Do you know the applications of different power amplifier circuits? Then, share your answers or views or doubts by posting your comments through the comments section below and further, technical assistance can be provided based on your comments.
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