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).
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
- Pulse amplifier
- Differential Amplifier
- Regulator circuits of electronic power supply
- Computer circuitry
- Jet engine control
- Electronic instruments