ELT 147 Digital Circuits
Experiment 1
(10 points)
Experiment 1
Bipolar Transistor Switch
Objective
To demonstrate the operation, characteristics and design of a saturated bipolar transistor switch.
Materials Required
Voltmeter (vom or DMM)
Digital Trainer (Refer to the Trainer manual for operations details and breadboarding procedures.)
1 - NPN transistor 2N2222
1 - 560 Ohm resistor
1- 1 kOhm resistor
1 - 4.7 kOhm resistor
1 - 10 kOhm resistor
1 - 220 kOhm resistor
Procedure
1 . Construct the circuit shown in Figure El-1 on the solderless breadboarding block. The circuit receives its
input from data switch SW1. You will monitor the output at the collector with a voltmeter. See Figure E1-2 for
transistor base details. When voltage is greater than 3.2 V this is considered to be a logic level HI. Values less
than 2.3 V is considered to be a logic Level LO
VCC
5V
R1
1.0kΩ
Output
J1
R2
220kΩ
C
B
E
Key = Space
Inverter circuit for Step 1. Lead connections for 2N2222 transistor
2.
Set SW1 to the down (LO) position and measure the DC output voltage (V(OUTPUT)) with respect to
ground. Record below.
V(output) =__________________ volts.
The input voltage at this time is
VI = _______________ volts.
3.
Set SW1 to the up (HI) position and measure the circuit DC input voltage (V1) with respect to
ground. Record below.
V1 =___________________ volts.
Next, measure the following transistor junction voltages base-to-emitter (VBE) base-to-collector (VCB). and
collector-to-emitter (VCE). Record your values in Table I using the RB = 220 kOhm row. Be sure to note the
polarity of each voltage so that you can determine whether the junctions are forward or reverse-biased.
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ELT 147 Digital Circuits
Experiment 1
(10 points)
RB
VBE
VCB
TABLE I
VCE=V(OUTPUT) Is the transistor
Saturated
220KOhm
4.7KOhm
4. Turn on Switch 1. easure the voltage drop across the 220 kOhm base resistor (VRB) and the voltage across
the collector resistor (VRC) and record in Table II in the RB = 220 kOhm column. Using these voltages and
associated resistor values, calculate the base current (IB.) and collector current (IC) using Ohm's law.
V
IB = RB
RB
IC =
VRC
RC
Record your values in Table II. Also calculate the ratio V. and record in Table II.
TABLE II
RB=4.7KOhm
RB=220KOhm
VRB
VRC
IB
IC
IC/IB
5. Using the criterion that states a transistor is saturated if the IC/IB < hFE, and the data in Table II, determine
the condition of the transistor assuming hFE = 100.
Is the transistor saturated? ____________________________
6. Replace the 220 kOhm base resistor R. with a 4.7 kOhm resistor.
7. Repeat Step 3. Measure VBE, Vc and VcE and record in Table 1. Study your results.
8. Repeat Step 4 recording your data in Table II.
9. Repeat Step 5.
Is the transistor saturated? _________________
2
ELT 147 Digital Circuits
Experiment 1
(10 points)
Experiment 2
Logic Inverter
Objective
To demonstrate the operation and characteristics of typical discrete component and integrated circuit logic
inverters.
Materials Required
DC Voltmeter
2 - 2N2222 transistor
2 -1 kOhm resistor
2 - 4.7 kOhm resistor
I - 74LS04 TTL hex inverter integrated circuit
1 . Wire the circuit shown in Figure E2-1. The input is derived from data switch SW1. You will measure the
output state with your voltmeter and observe it on LED indicator L1
VCC
5V
R1
1.0kΩ
J1
R2
4.7kΩ
C
LED
L1
B
E
Key = Space
Figure E2-1
2. Measure the inverter input and output voltages V, and V(output) with respect to ground for both positions
of data switch SW1. Record your data in Table 1
3.
From the data in Table 1, answer the following questions.
a. Does the circuit perform logic inversion? _______________________
b. What are the two output logic voltage levels assuming positive logic?
binary 0__________________
binary 1 _________________
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ELT 147 Digital Circuits
Experiment 1
(10 points)
4.
Disconnect the 4.7 kOhm base resistor from input SWI and let it hang free.
Measure the output voltage. V(output) __________________
With an open input, the output is binary ____________.
An open input has the same effect as a binary ______________ input. (Use positive logic.)
VCC
5V
R1
1.0kΩ
LED L2
XFG1
Agilent
R2
C
LED
L1
B
4.7kΩ
E
Figure E2-2
5. Connect the free end of the 4.7 kOhm base resistor to the CLK output and set the clock frequency to lHz.
Connect LED indicators to the circuit inputs and outputs as shown in Figure E2-2. Observe the operation of the
circuit by watching the LED indicator states and their relationship to one another. The circuit output is always
the______________of the input.
6. Mount a 74LS04 hex inverter IC (part number 443-755) on the bread- boarding block and connect pin 14
to +5 volts and pin 7 to ground (GND).
7. Connect one of the inverters as shown in Figure E2-8. The input will come from data switch SW1 and the
output will be displayed on indicator LED L1.
8. Apply the logic voltages to the input as shown in Table III and measure the corresponding output voltages.
Record in Table Ill.
Does the circuit invert? ______________________
What are the output voltage levels for positive logic?
volts
binary 0 =
binary I =
.volts
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