Experiment No:08
BJT parameters on DC biasing of BJT amplifier circuits.
A BJT bias stabilization circuit is a type of biasing circuit that is used to maintain a
stable operating point for the transistor. It typically includes a resistor and a biasing
voltage source that are connected to the base of the transistor. The resistor
provides a fixed current to the base, while the biasing voltage source provides a
fixed voltage.
There are different types of BJT bias stabilization circuits, including fixed bias,
emitter bias, voltage divider bias, and collector feedback bias One of the main
advantages of using a BJT bias stabilization circuit is that it provides a stable
operating point for the transistor, which can ensure reliable and consistent
performance over time.
Apparatus:
• Regulated DC power supply
• Resistor 1Mohms and 2.2K ohms.
• 2N3904 BJT transistor.
• Breaboard,DMM
Procedure:
• Design the BJT amplifier circuit, including the bias stabilization circuit. Choose
the resistor values based on the desired operating point for the BJT and the
specific requirements of the application.
• Build the circuit on a breadboard or PCB, connecting the BJT, resistors, and
power supply as indicated in the design. Use appropriate connectors and wires.
• Apply power to the circuit and measure the DC voltage and current at various
points in the circuit, using oscilloscope. Check that the biasing circuit is
providing the correct voltage and current levels to the BJT.
• Apply an AC signal to the input of the amplifier, using a function generator.
Measure the output signal at the output of the amplifier, using an oscilloscope.
• Adjust the biasing circuit to change the operating point of the BJT, and observe
the effect on the output signal. Note any changes in the gain, distortion, or other
parameters of the amplifier circuit.
• Repeat step 5 for different biasing conditions, and record the results. Analyse
the data to determine the optimal biasing conditions for the amplifier circuit.
• Optionally, compare the performance of the BJT amplifier circuit with other
types of amplifiers or biasing circuits, and discuss the advantages and
disadvantages of each.
Circuit Diagram:
Using 2N3904 transistor
Using 2N3055 transistor
Working:
The behaviour of the change of BJT parameters on DC biasing of BJT amplifier circuits
can be studied by varying the BJT parameters such as Beta (β), Vbe, and Ic to observe
their effects on the DC biasing of the amplifier circuit. The following steps can be
followed:
1. Design a BJT amplifier circuit with DC biasing and calculate the resistor values
based on the desired operating point of the BJT.
2. Build the circuit on a breadboard or PCB and connect a power supply to provide
DC voltage.
3. Measure the DC voltage and current at various points in the circuit, using a
multimeter or oscilloscope.
4. Vary the Beta (β) of the BJT by using a transistor with a different value or by
changing the temperature of the BJT. Observe the changes in the DC biasing
of the amplifier circuit.
5. Vary the Vbe of the BJT by changing the temperature of the BJT or by adding
a voltage source to the base of the transistor. Observe the changes in the DC
biasing of the amplifier circuit.
6. Vary the Ic of the BJT by changing the supply voltage or by changing the load
resistor in the collector circuit. Observe the changes in the DC biasing of the
amplifier circuit.
7. Record the results and analyze the data to determine the effects of changing
the BJT parameters on the DC biasing of the amplifier circuit.
Calculations:
Output Voltage: 10.9V.
Without heating output voltage: 9V
With heat output voltage: 8V.
Conclusions:
In conclusion, the behaviour of the change of BJT parameters on DC biasing of BJT
amplifier circuits can have significant effects on the performance of the amplifier circuit.
By varying the
Beta (β), Vbe, and Ic of the BJT, we observed changes in the DC biasing of the
amplifier circuit, such as changes in the quiescent point, gain, and stability.
