Hello friends, in this article we will know that TransformerWhat is a Transformer coupled transistor amplifier? What are the advantages of a transformer-coupled transistor amplifier? What are the disadvantages of a transformer-coupled transistor amplifier? And you will know about many facts related to it.
Transformer – Coupled Transistor Amplifier | Transformer coupled Transistor amplifier
The main reason for the low voltage and power gain of an RC coupled amplifier is that the effective load (RC) of each stage is reduced due to the low resistance introduced by each stage’s input to the preceding stage. If the effective load resistance of each phase can be increased, the voltage and power gain can be increased.
This transformer can be obtained by coupling. Using the impedance changing properties of transformers, the low resistance of one phase (or load) can be represented as the high load resistance for the previous phase. Transformer couplings are usually used when the load is low.
It is mostly used for power amplification. Figure 37.8 shows the two stages of a transformer-coupled amplifier. A coupling transformer is used to feed the output of one stage to the input of the next stage. The primary P of this transformer is made the collector load and its secondary S gives the input to the next stage.
Operations | Operation
When an AC signal first Transistor This coupling appears as amplified across the primary P of the transformer. The voltage developed in the primary is transferred by the transformer secondary to the input of the next stage as shown in Fig. 37.8. The second stage provides amplification in exactly the same way.
frequency response | Frequency Response
The frequency response of a transformer coupled amplifier is shown in Fig. 37.9. It is clear that the frequency response is rather poor i.e. the voltage gain is only constant over a small range of frequency. The output voltage is equal to the collector current multiplied by the reactance of the primary.
At low frequencies, the reactance of the primary starts to decrease, resulting in reduced gain. At high frequencies, the capacitance between the windings of the windings acts as a bypass condenser to reduce the output voltage and hence gain.
Hence, it follows, that there will be disproportionate amplification of frequencies in a complete signal like music, speech etc. Therefore, a transformer-coupled amplifier introduces frequency distortion. It may be added here that in a properly designed transformer, it is possible to obtain a fairly constant gain over the audio frequency range.
But a transformer that achieves a frequency response comparable to RC coupling can cost 10 to 20 times more than an inexpensive RC coupled amplifier.
- No signal power is lost across the collector or base resistors.
- An excellent impedance matching can be achieved in a transformer coupled amplifier. It is easy to make the primary’s inductive reactance equal to the transistor’s output impedance and the secondary’s inductive reactance equal to the next stage’s input impedance.
- Due to excellent impedance matching, transformer coupling provides high gain. As a matter of fact, one stage of properly designed transformer-coupling can provide the advantage of two stages of RC coupling.
- It has poor frequency i.e. the gain varies greatly with frequency.
- Coupling transformers are heavy and quite expensive on audio frequencies.
- Frequency distortion is high i.e. low frequency signals are less amplified as compared to high frequency signals.
- Transformer coupling introduces hum at the output.