Difference Between Voltage Amplifier and Power Amplifier

Voltage and power are the two major classifications of amplifiers and the classification is done on the basis of the comparison made according to the characteristics of applied input and generated output signal. The crucial difference between a voltage amplifier and a power amplifier is that a voltage amplifier increases the voltage level of the applied input signal. As against, a power amplifier is the one that boosts the power level of the input signal.

What is an Amplifier?

An amplifier is an electronic device that boosts the level of the signal present at its input and provides the raised but identical signal at the output. Thus, it is a device that serves the purpose of amplification. The factor that determines the level of the amplification given by the amplifying unit is known as the gain of the amplifier.

Generally, various applications require very large output signals which a single amplifying unit fails to provide. So, sometimes there is a cascade connection of amplifiers in which the output of one, acts as input to the next and so on. In this way, we get multistage amplification of the signal. Here in this article, we will discuss the differentiating factors between voltage and power amplifiers.

Content: Voltage Amplifier Vs Power Amplifier

  1. Comparison Chart
  2. Definition
  3. Key Differences
  4. Conclusion

Comparison Chart

Basis for ComparisonVoltage AmplifierPower Amplifier
BasicIt raises the voltage level.It provides increase in the power level.
Known asSmall signal amplifierLarge signal amplifier
Magnitude of input signalSmallComparatively large
Type of coupling usedRC couplingTransformer coupling
Base regionThe base region of transistor is thin.Here the base of transistor is comparatively thicker.
Value of ICLow, approximately around 1 mA.Quite high, nearly 100 mA.
Achieved ac powerLowVery high
Value of βLow (5 to 20)High (100)
Physical size of transistorSmallGenerally large
Heat dissipationLess More
Load impedanceHigh (4 kΩ to 10 kΩ)Low (5 to 20 Ω)

Definition of Voltage Amplifier

Here the name itself is indicating that it is an amplifier whose operation is associated with voltage. So, an amplification unit is designed to increase the level of voltage of the applied input signal and it is known as a voltage amplifier.

Its design is based on achieving the highest possible voltage gain. The gain of an amplifier is nothing but the ratio of output to the input value. The voltage gain of this amplifier is the ratio corresponding to the output voltage to the input.voltage vs power amplifier eq1

Suppose if the applied input signal voltage is 1 V and the output voltage after amplification is 25 V then the voltage gain will be 25, where the gain is a unitless quantity. These amplifiers are the device that draws a very little amount of power from the load. These are referred as small-signal amplifiers as here the magnitude of the signal which is actually given as input is very small which is raised by the amplifier circuit.

Definition of power amplifier

A power amplifier is a device that is designed to boost the power level of the signal present at the input. Basically, to have large power at the output, a signal having a large magnitude of signal voltage must be present at the input. This is the reason generally a voltage amplifier is present before a power amplifier.

Now some questions must be answered like what is the need for such a high voltage signal at the input and do you actually think that power can be amplified?

The answer to both the questions is that power can never be directly amplified as no device can do so. Basically, a power amplifier changes the dc power collected from an output circuit into an ac signal power. The high signal voltage at the input generates a high signal current, the product of which provides high output power.

As the ac power is controlled by the applied input signal, this is the reason, the power amplifier is regarded as a dc to ac power converter whose value is controlled by the input signal.

So, the power gain of the amplifier will be:

voltage vs power amplifier eq2

Wherevoltage vs power amplifier eq3

andvoltage vs power amplifier eq4

Key Differences Between Voltage Amplifier and Power Amplifier

  1. The voltage amplifier is designed to amplify voltage while the power amplifier amplifies the power level of the signal.
  2. Voltage amplifiers have an input signal of small magnitude thus is known as a small-signal amplifier. Whereas power amplifiers require input signal of comparatively larger magnitude thus is known as a large-signal amplifier.
  3. The base of the transistor in the voltage amplifier circuit is thin as it does not design to handle the large current. But as a power amplifier must handle large current, therefore, has a comparatively thicker base region.
  4. Generally, low or medium power transistors that have a smaller physical size is used to design a voltage amplifier. However, high power transistors having a large physical size is used for power amplifiers.
  5. In the case of the voltage amplifier, the value of the collector current is quite low, ranges nearly 1 mA. While for power amplifiers the collector current is a high value of around 100 mA.
  6. The amount of ac output power delivered by the power amplifier is quite high in comparison to the ac output power provided by the voltage amplifier.
  7. The current gain offered by a voltage amplifier is lesser than that offered by the power amplifier.
  8. A voltage amplifier is RC coupled whereas a power amplifier is transformer coupled.
  9. The load impedance of a power amplifier with a value of nearly 5 to 20 Ω is comparatively less than that of a voltage amplifier with a range between 4 to 10 KΩ.
  10. The heat dissipation is less in the case of a voltage amplifier than a power amplifier. Therefore, a cooling system is necessary for a power amplifier rather than a voltage amplifier.


Hence the above discussion concludes that both voltage and power amplifiers have their own operating zones based on the advantages offered by the two. A voltage amplifier gives a raised value of the input value as output. While for a power amplifier the product of current and voltage achieved at the output is higher than that present at the input.

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