Direct Coupled Amplifier

As shown in the below diagram, the direct coupled amplifier (DC) is consist of two transistors Q1 and Q2 , a voltage divider base bias resistor network (R1, R2) which is provided on the transistor Q1 base two collector resistors RC1and RC2, the transistor Q2 is self biased, we also use tow emitter bypass resistors RE1and RE2. The direct-coupled amplifier is operated without the using of frequency sensitive component like capacitor, inductor and Transformer etc. The direct coupled amplifier amplify the A.C signal with frequency as low a fraction of Hertz (Hz).

Direct Coupled Amplifier
Direct Coupled Amplifier

First of all when we applied a +ve half cycle at the I/P of Q1 transistor, which is already biased through the divider bias network. The +ve half cycle forwarded bias the transistor Q1 which start the conduction and give an inverted and amplified O/P  at the collector . As we know that,

VCE= Vcc - IcRc

This amplified -ve signed is provided to the base of Q2 transistor, which is self-bias (because they are connected in cascade condition). The base  of Q2 transistor  is a reversed  and did not  conduct,  the O/P of transistor Q2 is amplified  signal  (inverting to I/P of Q2) when the Q2 did not  conduct and the voltage  drop across collector  emitter  will be zero, therefore  the VCC is equal  to IcRc.

The O/P equal  to the voltage  drop  across the collector  resistors.

Applications of Direct Coupled Amplifier

  1. Pulse amplifier 
  2. Differential Amplifier
  3. Regulator circuits of electronic power supply
  4. Computer circuitry
  5. Jet engine control
  6. Electronic instruments