Difference Between Voltage and Power Amps

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Difference Between Voltage and Power Amps

Difference Between Voltage and Power Amps is somewhat artificial since useful power (i.e.
product of voltage and current) is always develop in the load resistance through which current
flows. The difference between the two types is really one of degree; it is a question of how much
voltage and how much power. A voltage amplifier is design to achieve maximum voltage amplification. It is, however, not important to raise the power level. On the other hand, a power amplifier is design to obtain maximum output power.

1.Voltage amplifier.

The voltage gain of an amplifier is give by:

A_v =β×R_C/R_IN

In order to achieve high voltage amplification, the following features are incorporate in such amplifiers:

(i) The transistor with high β ( >100) is use in the circuit. In other words, those transistors are
employed which have thin base.
(ii) The input resistance Rin of the transistor is sought to be quite low as compared to the
collector load RC.
(iii) A relatively high load RC is use in the collector. To permit this condition, voltage amplifiers
are always operated at low collector currents (j 1 mA). If the collector current is small, we can use
large RC in the collector circuit.

2.Power amplifier.

A power amplifier is require to deliver a large amount of power and as such it has to handle large current. In order to achieve high power amplification, the following features are incorporate in such amplifiers :

(i) The size of power transistor is make considerably larger in order to dissipate the heat produced in the transistor during operation.

(ii) The base is make thicker to handle large currents. In other words, transistors with comparatively smaller β are use.

(iii) Transformer coupling is use for impedance matching.

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