THE TRANSISTOR-RESISTOR
EQUIVALENT CIRCUIT
EXPERIMENT NO. 1
EXPERIMENT NO. 1
DATE PERFORMED Expt. No. 1:
DATE SUBMITTED Expt. No. 1:
THE TRANSISTOR-RESISTOR EQUIVALENT CIRCUIT
OBJECTIVES:
1. to demonstrate the resistor-equivalent of a transistor in an amplifier circuit
2. To observe how the CE amplifier output current and voltage are relate
d to each other.
BACKGROUND INFORMATION:
A review of what happens in a normal DC resistive circuit should help somewhat, before commencing the study of amplifiers. It gives the experimenter a feeling for what he supposed to be looking for.
In this case we are connected of what is going to happen in the output circuit of a transistor amplifier, and so first it will be simulated with resistors. Notice for example the figure shown below. The transistor is in series with a load resistance; therefore, a voltage division will occur as current passes through the load and the transistor.
Ideally, at the correct operating current, the voltage across each of
these resistances should be identical, that is, one half of the supply voltage. As the resistance of the transistor charges with a signal input, the voltage will also change, giving you an output voltage that tracks the input voltage.
MATERIALS REQUIRED:
Power Source: Regulated Power Source
Equipment: DVM, 0-5mA ammeter
Components:
Resistor: - 4.7kΩ
Potentiometer: - 10kΩ
Miscellaneous: protoboard , connecting wires, and long nose pliers.
PROCEDURES:
1. Connect the circuit shown below. Notice that the 10kΩ potentiometer replaced the transistor in Figure 1-1 and will simulate its function.
2. Turn ON the power source and adjust the potentiometer resistance until the current registers 1.0mA. Measure the voltage V1 and record it in Table 1-1
3. Repeat the Measurements each value of current as indicated in Table1-1
4. When the measurements are completed and before turning OFF the power, measure and record the actual supply voltage. Compute and record the voltage across the load for each point in table1-1.
5. Measure the resistance of the load resistance and record it in Table1-1.
Table1-1
| I,mA | 1.0 | 1.2 | 1.4 | 1.6 | 1.8 |
| V1 | 4.4v | 2.7v | 2.22v | 1.9v | 0 |
| VRL | 3.9v | 5.6v | 6.1v | 6.5v | 8.4 |
CONCLUSIONS:
QUESTIONS:
1. When the circuit was 1.0 mA, was the voltage across the load resistor equal to the voltage across the potentiometer?
2. As the voltage increases across the load resistance, what happens to the voltage across the potentiometer which is simulating the transistor?
3. What should be the collector-to-emitter voltage at the main point of operation (IC=1.0mA) if a transistor was substituted for the potentiometer?
4. If a transistor was substituted for the potentiometer, what should be its resistance at 1.9 mA of circuit current?
