Power Amplifiers Transformerless Power Amplifier

Power amplifiers

Power amplifiers are an independent group of electronic devices that have special properties: they can amplify both current and voltage to obtain the required power at the load, and also have an output impedance consistent with the impedance of the electrical energy receiver.
The output impedance of the amplifier stage, in which the transistor is connected according to the scheme with a common emitter (or common source), amounts to hundreds of ohms or units of kOhms, while the resistance of the load device consuming *** high power is units to tens of ohms. With such a ratio of resistances, the power allocated to the load device is determined by the formula , which follows from the analysis of the equivalent circuit, Figure 4.



The load devices of power amplifiers are:
• windings of electric motors
• relay
• loudspeakers and other elements of electrical circuits that have small resistances (from 1 to 10 ohms)
In these devices requires a significant power amplified signal (from 10 to 100 W)
• The main indicator - power gain factor Kp = Ku • KI
• Obtaining the required power in the load device is ensured by selecting the appropriate transistor and the equality Rout of the device = Rn
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• a step-down transformer
• emitter follower

Transformerless Power Amplifier


Figure 5 Power Amplifier - Push Pull
Power amplifier - push-pull figure 5 is assembled on transistors of different types of electrical conductivity:
T1 - type n – p – n; T2 - type p – n – p
T1 and T2 are included under the scheme with OK; it is necessary that transistors of different types have exactly the same parameters. If using discrete elements, then take complementary pairs of transistors.