Direct Coupled Amplifier – Circuit Diagram, Operation | New Topic [2024]

In this note, we are going to learn about Direct Coupled Amplifier, about its circuit diagram, operation, advantages, disadvantages, and applications also. Welcome to Poly Notes Hub, a leading destination for engineering notes for diploma and degree engineering students.

Author Name: Arun Paul.

About Direct Coupled Amplifier

Many applications require extremely low-frequency signals to be amplified, such as amplifying photoelectric current, thermocouple current, and so on. Coupling devices such as capacitors and transformers are ineffective because their electrical sizes increase dramatically at extremely low frequencies. In such cases, one stage is directly connected to the following step, with no intervening coupling device. This sort of coupling is referred to as direct coupling.

Direct Coupled Amplifier Circuit Diagram

Figure displays the circuit of a three-stage direct-coupled amplifier. It employs a complementary transistor. Thus, the first stage employs a NPN transistor, the second a PNP transistor, and so on. This arrangement makes the design quite easy.

Working of Direct Coupled Amplifier

The output from the collector of first transistor T1 is fed to the input of the second transistor T2 and so on.

The weak signals is applied to the input of first transistor T₁. Due to transistor action, an amplified output is obtained across the collector load R_C of transistor T₁. This voltage drives the base of the second transistor and amplified output is obtained across its collector load. In this way, direct-coupled amplifier raises the strength of weak signal.

Advantages of Direct Coupled Amplifier

Here are some merits of this type of amplifier –

• The circuit design is very simple.
• The circuit has low cost.

Disadvantages of Direct Coupled Amplifier

Here are some demerits of this type of amplifier –

• This circuit cannot be used for amplification of high frequency.
• The operating point may be shifted due to temperature variations.

Application of Direct Coupled Amplifier

Here are some uses of this type of amplifier –

• Used in ECG and EEG medical mechines.
• Used in Analog computers.
• Used in Audio Amplifiers and Control Systems.