DC Amplifier : Circuit Diagram, and Applications

An Amplifier circuit can be described as, a circuit which is used to increase the input signal. But, not every amplifier circuit is the same due to their type of circuit configuration as well as operation. In electronic circuits, a small signal amplifier can be used because it amplifies a small input signal. There are different types of amplifier circuits like operational amplifiers, power amplifiers, and small signal to large signal amplifiers. The amplifiers classification can be done based on the signal size, configuration and process of the input signal which means the relationship among the flow of current within the load as well as an input signal. This article discusses an overview of DC amplifiers.

What is a DC Amplifier?

A DC amplifier (direct coupled amplifier) can be defined as is a kind of amplifier where the one stage output of the amplifier can be connected to the next stage input for allowing the signals without frequency. So this is named as the direct current which passes from input to output. The DC amplifier is another type of coupling amplifier and this amplifier is particularly used for amplifying low-frequencies like thermocouple current otherwise photoelectric current.

DC Amplifier
DC Amplifier

This type of amplifier can be used for both DC (direct current) signals as well as AC (alternating current) signals. The DC amplifier’s frequency response is the same as LPF (low pass filter). The direct current amplification can be achievable only by using this amplifier, therefore later it turns into the basic building block of the differential as well as operational amplifier. In addition, monolithic IC(integrated circuit) technology does not permit the production of large coupling capacitors.

Direct Coupled Amplifier Circuit

The construction of DC (Direct Coupled) Amplifier Circuit is shown below. The circuit can be built with two transistors namely Q1, and Q2. A bias resistor network (R1, R2) based on voltage divider which is connected on the primary transistor base terminal & collector resistors such as R1, and R2. The secondary transistor Q2 in the above circuit is self-biased and this circuit also uses bypass transistors like RE1 & RE2.

Direct Coupled Amplifier Circuit
Direct Coupled Amplifier Circuit

The DC amplifier circuit can be operated without using capacitors, transformer, inductor, etc which is known as frequency sensitive components. This amplifier amplifies the AC signal by low frequency. Whenever we applied a positive half cycle at the input of the primary transistor Q1. This transistor is already biased with the help of the divider bias network. The applied half cycle can make the Q1 transistor forward biased to start the conduction & provide an amplified and inverter output the collector terminal.



This negative signed amplified signal is given to the base terminal of the second transistor (Q2). Here this transistor is also self-biased. The Q2 transistor’s base terminal can be reversed as well as didn’t conduct, the Q2 transistor output can be an amplified signal as the transistor doesn’t conduct as well as the drop of voltage across CE-collector emitter will be nothing (zero), thus the VCC is equivalent toward ICRC.

Frequency Response of DC Amplifier

There are different types of amplifiers available, where all these amplifiers have a common cut-off frequency of an upper as well as a lower. A DC amplifier has a direct current frequency like the lower limit.

In theory, we actually don’t know the lower boundary as the amplifier can pass a frequency whose period is 1/( time duration). The higher limit is generally defined when the location of the frequency is under the middle point then the frequency will be -3dB. Whenever the frequency range is above the middle point then the output will continue to reduce the amplitude. From the above statement, we can conclude that the amplifier was intended for flat frequency response.

Characteristics of Different Types of Coupling Methods

There are three types of coupling methods are available like RC Coupling, Transformer Coupling, and Direct Coupling. The characteristics of these amplifiers include the following.

Frequency Response

  • The frequency response of RC coupling is outstanding within the audio frequency range
  • The frequency response of transformer coupling is poor
  • The frequency response of the direct coupled amplifier is best.


  • The cost of RC coupling is less
  • The cost of transformer coupling is more
  • The cost of direct coupling is least.

Space and Weight

  • The space and weight of RC coupling is less
  • The space and weight of transformer coupling is more
  • The space and weight of direct coupling are least.

Impedance matching

  • The impedance matching of RC coupling is not good
  • The impedance matching of transformer coupling is excellent
  • The impedance matching of direct coupling is good.


  • The use of RC coupling is for voltage amplification
  • The use of transformer coupling is For Power amplification
  • The use of direct coupling is for amplifying extremely low frequencies.

Advantages of DC Amplifiers

The advantages of DC amplifiers include the following.

  • This is a simple circuit and can be designed a minimum number of basic electronic components
  • It is inexpensive
  • This amplifier can be used to amplify low-frequency signals

Disadvantages of DC Amplifiers

The disadvantages of DC amplifiers include the following.

  • In DC amplifier DRIFT can be examined, which an unnecessary transform within o/p voltage without changing its input voltage.
  • The output can be changed by the time or the age & modify in supply voltage.
  • The transistor parameters β & vbe can change by temperature. This can cause the change within CC (collector current) & voltage. Thus, the o/p voltage can be changed.

Applications of DC Amplifiers

The applications of DC amplifiers include the following.

  • The applications of DC amplifiers include computers, regulator circuits¸ TV receivers, and other electronic devices.
  • This amplifier can build differential amplifiers as well as operational amplifiers.
  • These amplifiers can be used in pulse amplifiers, differential amplifiers,
  • These amplifiers can be used in controlling of Jet engine, regulators in power supply. etc

Thus, this is all about the DC amplifier. From the above information, finally, we can conclude that in this amplifier, the amplifier’s one stage output is connected to the amplifier’s next stage input by allowing signals by zero frequency. Here is a question for you, what is the working of DC amplifier?