Difference Between Power Amplifier and Voltage Amplifier

Power Amplifier vs Voltage Amplifier
 

Amplifiers are devices used in electronics, to improve or multiply the strength of a signal. Depending on the requirements amplifiers are used to increase the voltage of the signal or the current of the signal or the power of the signal. Generally amplifiers are 3 port devices, with an input port, an output port and a power supply port. Generic operation of an amplifier is to produce a strengthened version of the input signal at the output, consuming the power from the power supply. The ratio between the output signal and the input signal of a property such as voltage, current or power is referred to as Gain. For example, ratio between output voltage and the input voltage is the Voltage gain of the amplifier GAINvoltage= Vout / Vin, and similarly GAINpower = Pout / Pin. For linear operation of an amplifier, as required in most cases, the gain values have to be constant in the region of operation.

Voltage Amplifier

Voltage amplifiers are devices that amplify the input voltage, if possible with minimal current at the output. Technically, an amplifier with high voltage gain is a voltage amplifier, but it may or may not have a low current gain. The power gain of an amplifier is also low due to these properties. Transistors, and op amps, given proper biasing and other conditions, act as basic voltage amplifiers. The main application of voltage amplifiers is to strengthen the signal to make it less affected by noise and attenuation. When transmitted signals lose its strength and get deformed, an amplification of the voltage at the transmitter will minimize the effect and receiver will be able to capture and interpret the signal with reasonable accuracy.

Ideal voltage amplifiers have infinite input impedance and zero output impedance. In practice, an amplifier with high input impedance relative to the output impedance is considered as a good voltage amplifier.

Power Amplifiers

Power amplifiers are devices to amplify the input power, if possible with minimal change in the output voltage with respect to the input voltage. That is, power amplifiers have a high power gain, but the output voltage may or may not change. The amplifier efficiency of power amplifiers is always lower than 100%. Therefore, high heat dissipation is observed at power amplification stages. Power amplifiers are used in devices which require a large power across the loads. In multi stage amplifiers, power amplification is made in the final stages of amplification. Audio amplifiers and RF amplifiers use power amplifiers at the final stage to deliver sufficient power the load. Servo motor controllers also use power amplifiers to drive the motors. Power amplifiers are classified into several classes depending on the fraction of the input signal used in amplification. Classes A, B, AB and C are used in analog circuits, while classes D and E are used in switching circuits.

In modern electronics, most power amplifiers are constructed with semiconductor based components while, vacuum tube (valve) based amplifiers are still used in environments, where precision, frequency response, and endurance are a primary requirement. For example, guitar amplifiers use valves for quality and military equipment use valves for its endurance against strong electromagnetic pulses.

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