Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 1
TESTING SEMICONDUCTOR DIODES & DIODE CHARACTERISTICS
Introduction:
Diode is the simplest of all electronic devices but it has limitless applications. A diode permits
current flow when the voltage on the anode is positive with respect to the voltage on the
cathode, and it inhibits current flow when the voltage on the anode is negative with respect
to the voltage on the cathode.
The characteristics of an ideal diode are those of a switch that can conduct current in only
one direction. A semiconductor diode conducts if it is in forward bias; that is the applied
voltage must be greater than zero.
Objectives:
1. To become familiar with multimeter, breadboard, oscilloscope, and writing circuit;
2. To test diodes using ohmmeter.
3. To display the diode characteristics using oscilloscope.
Materials needed:


Standard or Digital Multimeter
Different types of diode
TESTING SEMICONDUCTOR DIODES
An ohmmeter has a low-voltage potential place at its leads when measuring resistance. One
lead is positive (usually red in color) and the other lead is negative (usually black in color).
When positive lead is placed on the anode of a diode and the negative lead on the cathode,
this forward resistance (Rf) should be low, since the diode is forward biased. When the leads
are reversed resistance (Rr) should be high, since the diode is reverse biased.
Procedure:
1. Refer to Figure 1-1.a and place the ohmmeter leads accordingly on the diode leads.
Figure 1-1.a
2.
3.
4.
5.
Figure 1-1.b
Set the ohmmeter to the lowest scale and record the Rf reading.
Refer to Figure1-1.b and place the ohmmeter leads accordingly on the diodes leads.
Set the ohmmeter to the highest scale and record the Rr reading.
Calculate the ratio of reverse to forward resistance from the formula.
Observation:
Result and Computations:
Fill-In Questions:
1. A forward-biased diode has
2. A reversed-biased diode has
resistance.
resistance.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 2
THE DIODE AS A SWITCH
Introduction:
Referring to Figure 1-2.a note that the forward-biased silicon diode has a voltage drop of 0.7V
across it with the remaining power supply voltage dropped across the load resistance (R L).
The voltage drop of RL can be found by the formula VL = Vdd - Vf . The forward current (IF)
through the circuit can be found by the formula ID = VL/RL. Referring to Figure 1-2b, note that
a reverse-biased silicon diode has the total power supply voltage dropped across it, while the
voltage drop across the load resistor is zero, since no current is flowing in the circuit.
Figure 1-2.a
Figure 1-2.b
Objective:
1. To recognize a conducting and non conducting diode by its circuit voltage drops;
2. To determine the forward current.
Apparatus/Materials:

1 Variable Low-Voltage power supply




1 Standard or Digital Voltmeter
1 1KΩ Resistor at 0.5W
1 n4001 Silicon Diode or Similar Type
1 Breadboard for constructing circuit
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Construct the circuit shown in figure 1-2a.
Set the power supply voltage at +6V.
Measure and record VF across the diode.
Measure and record VL across RL.
Calculate ID and record.
Turn the diode around as shown in figure 1-2b.
Measure and record VF across the diode.
Measure and record VL across the RL.
Calculate ID and record.
Observations:
Results and Computations:
Fill-in Questions:
1. The forward voltage across a silicon diode in a normally working circuit
is
V.
2. A resistor in series with the diode of question 1 would have voltage drop equal to the
minus the voltage drop of the
.
3. If the diode in question 1 were to open, the voltage drop across it would be
V. (Hint: refer to figure 1-2b)
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 3
CURRENT – VOLTAGE CHARACTERISTICS OF A DIODE
Introduction:
As the forward voltage across a diode increase, so does the forward current. Unlike a
fixed resistor, a semi conductor junction’s resistance decreases with an increase in current
flow because of the increase in electron-hole combinations. The forward resistance of a
conducting diode can be found by the Ohm’s Law Calculation Rf = Vf / If. The voltage across
the entire circuit can increase to several volts, while the external load resistor (R1) mainly
determines the current flowing in the circuit. In the reverse-biased condition, there is very
little current (µA) flow, and hence the reverse resistance is high. The reverse resistance of a
diode can be found by Ohm’s Law Calculation RR = VR / IR.
Objective:
1. To demonstrate the relationships of forward voltage, current and resistance of a diode,
and the reverse voltage, current and resistance.
Apparatus/Materials:






1 Variable Low-Voltage power supply (VP to 20V)
1 Standard or Digital Voltmeter
1 standard or Digital DC Current Meter
1 1N4001 silicon diode or similar type
1 1-KΩ Resistor at 0.5W
1 Breadboard for constructing circuit
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Construct the circuit shown in figure 1-3a.
Adjust the variable power supply for a Vf reading of 0.1V.
Record If in the second column of data table 1.
Calculate Rf from the two values given and record in the third column of data table 1.
Repeat steps 2, 3 and 4 for the Vf values given in data table 1 up to 0.8 B.
Set the variable power supply to zero and reverse its leads as shown in figure 1-3b.
Reverse the leads of the meters.
Adjust the variable power supply for a VR reading of -2V.
Record IR in the second column of data table 2.
10. Calculate RR from the two values given and record in third column of data table 2.
11. Repeat steps 8, 9 and 10 for the VR values given in data table 2 up to -20V.
12. From the values of VF and IF in data table 1 and the values of VR and IR in data table 2, plot
a graph in figure 1.3c.
Fig. 1.3a
Fig. 1.3b
Data Table
1
Data Table
2
VF
IF (mA)
RF = VF/IF
VR
IR (mA)
RR = VR/IR
0
0
∞
0
0
∞
0.1
-2
0.2
-5
0.3
-7
Fig. 1.3c
Observations:
Results and Computations:
Fill-in Questions:
1. When the forward current of a diode increases, its forward resistance
2. The current flowing in a diode circuit is determined primarily by the
3. The in a reverse-biased diode circuit is extremely
, while the
resistance of the diode is extremely
.
.
.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 4
DIODE VOLTAGE DROPS
Introduction:
The voltage drop across a forward-biased is about 0.7V. this voltage drop is somewhat
stable, and in some instances diodes are placed in series to develop a reference voltage. In
this experiment, you will measure the voltage drops across diodes in series.
Objective:
1. To demonstrate how voltage drops across diodes in series are additive and to show the
shorting effect of a forward-biased diode.
Apparatus/Materials:








1 Variable Power Supply
1 Standard or Digital Voltmeter
1 Dual-Trace Oscilloscope
1 Sine-wave Generator or Function Generator
1 100-Ω Resistor at 0.5W
1 1-KΩ Resistor at 0.5W
3 1N4001 Silicon Diode or Similar type
1 Breadboard for constructing circuit
Procedure:
1. Construct the circuit shown in figure1-4a.
2. Apply power to the circuit.
3. With the voltmeter, measure the voltage across each diode and record here.
V1 =
, V2 =
, V3 =
.
4. Place the black lead of the voltmeter on ground.
5. With the red lead, measure the voltage across D1, as shown by M1. Record the value
here:
. It should be the same as V1.
6. Measure the voltage across D1 and D2 in series as shown by M2. Record the value here:
. It should be the same as V1 + V2.
7. Measure the voltage across D1, D2 and D3 series as shown by M3. Record the value here:
. It should be the same as V1 + V2 + V3.
FIG 1-4a
FIG 1-4b
8. Construct the circuit shown figure 1-4b.
9. Set the Sine-wave Generator for 1 KHZ and amplitude of 2V.
10. Place one channel of the oscilloscope across VIN.
11. Place the other channel of the oscilloscope across the VOUT of the circuit.
If a forward-biased diode is placed in parallel with a resistor of some resistance, nearly not all
of the current will flow through the diode. In other words, in forward-biased condition the
diode “short out” the resistor. If the diode is reversed, the diode has an extremely high
resistance and most of the current will flow through the resistor, developing a voltage drop.
Notice that only the negative alternation is seen at the output of the circuit. When the
positive alternation is present, the diode conducts and only a 0.7V line appears across on the
face of the CRT. When the negative alternation is present, the diode does not conduct and
the current flows through the resistor, developing the negative-going voltage.
Results and Computations:
Fill-in Questions:
1. The voltage drop of forward-biased diodes in series is
.
2. In four silicon diodes are forward-biased and connected in series, the total voltage drop
across them will be
volts.
3. A forward-biased diode has
resistance and will allow a
current to flow through it.
4. A reverse-biased has
or infinite resistance and allows little or
current to flow through it.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 5
HALF-WAVE RECTIFICATION
Introduction:
Refer to figure 1-5 and note that when point A of T1 is positive point B will be negative.
The diode will be forward biased, and the current flow from point B up through RL, through
D1 to point A and the transformer, developing a positive going output voltage waveform
across RL. When point A is negative, point B will be positive, the diode is reversed-biased, no
current flows, and there is no voltage output across RL. Therefore, the output voltage is
positive pulsating do, which can be filtered with capacitors in an attempt to produce pure DC.
Objective:
1. To demonstrate how a diode will rectify (or pass) only one alternation of a sine wave
Apparatus/Materials:





1 Oscilloscope
1 12- or 24- V Center-tapped transformer (T1)
1 1N4001 Diode (D1) or similar type
1 10KΩ resistor at 0.5W (RL)
1 Breadboard
Procedure:
1. Before applying power, construct the circuit shown in figure 1-5.
Vout = _______ V p-p
FIGURE 1-5
2. Apply power to the circuit.
3. Place the oscilloscope across RL, observing polarity.
4. Record the amplitude of the voltage seen on the oscilloscope in the location marked
VOUT =
.
5. Remove power from the circuit.
6. Turn the diode around the circuit.
7. Apply power to the circuit.
8. Observe the oscilloscope and draw the output waveform, indicating its amplitude:
VOUT =
.
The diode is now passing the negative alternation of the sine wave, and the polarity across
RL has been reversed. The voltage can be used to develop negative DC supply voltage.
Observations:
Results and Computations:
Fill-in Questions:
1. A diode will pass only
alternations of a sine wave.
2. A half-wave rectifier can produce positive or negative pulsating DC, depending on the
that the diode is placed in the circuit.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 6
FULL-WAVE RECTIFICATION
Introduction:
Refer to the figure 1-6, note that when point A of T1 is positive, point B is negative.
Diode D1 is forward biased, and current flows from the center tap of T1, up through RL.
through D1 to point A and the transformer. This develops a positive-going voltage across RL.
Diode D2 is reversed biased and no current flows through it. When point A is negative, pint B
will be positive. Diode D2 is now forward biased and current flows from the center tap, up
through R1 through D2 to point B and the transformer. Since the current is in the same
direction through R1 for this alternation, a positive going voltage is again developed across
RL. Diode D1 is reversed biased and no current flows through it. This voltage output is much
easier to filter with capacitors in an attempt to produce pure DC.
Objective:
1. To show two diodes pass both alternations of sine wave to prove a better pulsation DC
voltage.
Apparatus/Materials:





1 Oscilloscope
1 12- or 24- V Center-tapped transformer (T1)
2 1N4001 Diodes (D1 and D2) or similar type
1 10KΩ resistor at 0.5W (RL)
1 Breadboard for constructing circuit
Procedure:
1.
2.
3.
4.
Before applying power, construct the circuit shown in figure 1-6.
Apply power to the circuit.
Place the oscilloscope across RL observing polarity.
Record the amplitude of the voltage seen on the oscilloscope in the location marked
VOUT.
5. Remove power from the circuit.
6. Turn both diodes around the circuit.
7. Apply power to the circuit.
8. Observe the oscilloscope and draw the output waveform, indicating its amplitude:
VOUT =
This is similar to the procedure in Experiment No. 5. The current is now reversed in RL and a
negative going pulsating DC voltage is developed.
Vout = ________ V p-p
FIGURE 6-1
Observations:
Results and computations:
Fill-in Questions:
1. A full-wave rectifier passes both
of a sine wave.
2. In terms of polarity, the output of a full wave rectifier has both alternations of the sinewave input voltage going in
the direction.
3. A full-wave rectifier can produce positive or negative DC, depending on the
the diodes are placed in the circuit.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 7
BRIDGE (FULL-WAVE) RECTIFICATION
Introduction:
Refer to figure 7a and notice how the diodes are connected and that they all point in
one general direction – to the right. When point A is positive, D2 is forward biased, while point
B is negative and D3 is forward biased. Diodes D1 and D4 are reversed biased at this time.
Current flows from point B through D3 up through RL, through D2 to point A and the
transformer. A positive going voltage waveform is developed across RL. when point A is
negative, point B is positive. Diodes D2 and D3 are now reversed biased, but diodes D1 and D4
are forward biased. Current now flows from point A and D1 up through RL, through D4 to point
B and the transformer. Since the current through RL is in the same direction, another positive
voltage waveform for this alternation of the sine-wave across the transformer. Full-wave
rectification is accomplished with this circuit without the use of the center tap of the
transformer.
Objective:
1. To demonstrate four diodes in a bridge arrangement produce wave rectification without
the use of a center-tapped transformer.
Apparatus/Materials:





1 Oscilloscope
1 12- or 24- V Transformer (T1)
4 1N4001 Diodes (D1 to D4) or similar type
1 10KΩ resistor at 0.5W (RL)
1 Breadboard for constructing circuit
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Before applying power, construct the circuit shown in figure 7a.
Apply power to the circuit.
Place the oscilloscope across RL, observing polarity.
Record the amplitude of the voltage seen on the oscilloscope in the location marked VOUT.
Remove power from the circuit.
Remove D1 from the circuit.
Apply power to the circuit.
Observe the oscilloscope and draw the output waveform, indicating its amplitude:
VOUT =
.
If one of the diodes in the bridge circuit is open, one of the alternation is lost at the output.
9. Compare the output voltage of all three rectifier and the bridge rectifier have the same
amplitude, however, the bridge rectifier will be easier to filter. The amplitude of the
standard full wave rectifier is one-half of the other two because of the center-tapped
transformer needed.
Vout = ________ Vp-p
FIGURE 7A
Observations:
Results and Computations:
Fill-in Questions:
1. The main advantage of the bridge rectifier over the standard full-wave is that it does not
require a
transformer.
2. When one of the diodes in the bridge circuit opens, one of the
will be missing at the output.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 8
POWER SUPPLY FILTERING
Introduction:
Refer to the figure 8a, note that when T positive-going pulse increases across RL the
capacitor C1 charges up to the peak voltage. When the pulse begins to decrease, the electrons
stores on the negative plate of C1 discharge through RL in attempt to keep the voltage
constant across RL, before the capacitor has the chance to discharge too far, another positivegoing pulse arrives to charge it up to peak voltage. Pure DC is now present at the output but
a smaller AC component known as ripple voltage is riding along the top of it, due to the
charging and discharging of the capacitor.
Refer to 8b and note that the same action occurs with both capacitors, they attempt
to keep the voltage across RL constant, however, they are not allowed to discharge as long as
before another positive going pulse is present due to the full-wave rectification. Resistor RS
separates the capacitors and provides better filtering action. The ripple voltage for this power
supply will be much less.
Objectives:
1. To show how capacitors attempt to filter pulsating DC and produce pure DC.
Apparatus/Materials:








1 Oscilloscope
1 12- or 24- V transformer (T1)
1 Standard or Digital Voltmeter
4 1N4001 Diodes (D1 to D4) or similar type
1 10-kΩ resistor at 0.5W (RL)
1 100-Ω resistor at 0.5W (RS)
2 470-µF Electrolytic Capacitors at 50WV
1 Breadboard for constructing circuit
Procedure:
1. Before applying power, construct the circuit shown in figure 8a.
2. Apply power to the circuit.
3. Place the voltmeter across RL observing polarity, and record the DC voltage in the location
marked VOUT.
4. Remove the voltmeter.
5. Set the input of the oscilloscope to AC and adjust its vertical input control to the lowest
setting.
Ripple Voltage = ________V p-p
FIGURE 8A
Ripple Voltage = ______ V p-p
FIGURE 8B
6. Place the oscilloscope across RL observing polarity and record the voltage amplitude
shown in the location marked ripple voltage.
7. Remove power from the circuit and disassemble the circuit.
8. Construct the circuit shown in figure 8b.
9. Apply power to the circuit.
10. Place the voltmeter across RL observing polarity and record the DC voltage in the location
marked VOUT.
11. Remove the voltmeter.
12. Place the oscilloscope across RL observing the polarity and record the voltage amplitude
shown in the location marked ripple voltage.
13. Remove power from the circuit.
14. Remove C1 from the circuit.
15. Apply power to the circuit.
16. Indicate if the ripple voltage remained the same, increased or decreased.
Ripple voltage
.
17. Remove power from the circuit.
18. Replace C1 and remove C2 from the circuit.
19. Apply power to the circuit.
20. Indicate if the ripple voltage remained the same, increased or decreased from the original
value in step 2. Ripple voltage
. which capacitor had the
most effect on the ripple?
.
Observations:
Results and Computations:
Fill-in Questions:
1. Capacitors in a power supply attempt to keep the DC output voltage constant by
through the load resistor.
2. Full-wave rectification is easier to filter than
rectification.
3. The ripple voltage for a full-wave power supply is
than for a
half-wave power supply.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 9
TESTING ZENER DIODES
Introduction:
An ohmmeter can detect a short or an open Zener diode in the same way as with a
regular diode. However, this test does not determine if the diode will operate properly at its
specified Zener voltage. A simple test can be performed on the Zener diode using a power
supply that has a higher voltage than the VZ of the diode. The power supply can be variable
or fixed, using a potentiometer to vary its voltage. The Zener diode is reverse biased by the
power supply. The power supply voltage is gradually increased. The voltage across the diode
will follow the increasing voltage until it reaches the VZ point, at which time an increase in
power supply voltage will have little effect to the VZ point of the diode.
Objective:
1. To demonstrate a practical method of testing Zener diodes with a power supply.
Apparatus/Materials:




1 Variable power supply up to +12V
1 Standard or Digital Voltmeter
1 100-Ω Resistor at 0.5W (RS)
1 1N5231 Zener diode (5.1V) or 1N960 (9.1V) or Equivalent.
For Alternating Circuit Include:


1 1-kΩ Potentiometer (Linear) (RA)
1 Breadboard for constructing circuit
Procedure:
1.
2.
3.
4.
5.
6.
Construct the circuit shown in Figure 9a or 9b depending on the power supply used.
Adjust the power supply to 0V.
Measure the VZ of the diode and record it in the voltage table of Figure 9c.
Adjust the power supply voltage to +1V.
Measure the VZ of the diode and record it in the voltage table.
Continue Steps 4 and 5 in 1-V increments up to +12V.
FIGURE 9a
Observations:
Results and Computations:
FIGURE 9b
+V
0
1
2
3
4
5
6
7
8
9
10
11
12
VZ
Figure 9c
Fill-in Questions:
1. The Zener diode is usually operated on the
condition.
2. The VZ of a Zener diode will
fairly constant even if the power supply
voltage
.
3. The series resistor RS is used with the Zener diode to
the Zener current
IZ to a
level.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 10
HOW THE ZENER DIODE OPERATES AS VOLTAGE REGULATOR
Introduction:
Refer to figure 208a and note that the total current (IT ) flowing through R S must be
determined when there is no load resistor (R L ) connected to points A and B. at this time IZ
equals IT . When a load resistor is connected to points A and B, current flows through the
Zener diode (IZ ) will decrease the necessary amount to keep IT constant as a result, VRS and
VZ will remain constant.
Objective:
1. To show how the Zener diode regulates the voltage across its terminals by varying the
current through it when there are varying load currents in the circuit.
Apparatus/ Materials:
 1 +12-V power supply
 1 Standard or digital ammeter
 1 standard or digital voltmeter
 1 IN960 Zener diode (9.1V) or equivalent
 1 100 – Ω resistor at 1.0 W (R S )
 1 500 - Ω resistor at 0.5 W (R L )
 1 1-kΩ resistor at 0.5 W (R L )
 1 2.2 kΩ resistor at 0.5 W (R L )
 1 4.7 kΩ resistor at 0.5 W (R L )
 1 10-kΩ resistor at 0.5 W (R L )
Procedure:
1. Construct the circuit shown in Figure 10a. Do not connect R L at this time and make
provisions for inserting the ammeter to read IZ and R L .
2. Calcite VRS from the Formula VRS = +V - VZ . Record VRS here: _______________.
3. Calculate IT from the formula IT = VRS /R S . Record IT here: _________________.
4. Apply power to the circuit; then measure IL , IZ , VRS , and VZ and record in the proper
places in the table at Figure 10b. Calculate IT and VT from the table and record I their
proper places.
5. Connect the 10-kΩ resistor to points A and B. Measure IL and record in the proper place
in the table.
6. Measure IZ and record in the proper place in the table.
7. Calculate total current from the formula IT = IL + IL using the data in the table and place
the answer in the proper place.
8. Measure VRS and VZ and record in the proper places in the table.
9. Calculate VT from the formula VT = VRS + VZ using the data in the table and place the
answer in the proper place in the table.
10. Repeat steps 5 through 9 for the various values of R L given in the I-V table.
Notice that for the 100-Ω resistor VZ decreases to +6V. in this case the load current (IL ) is
so large that the Zener diode current IZ decreases below its minimum holding level and the
Zener diode electricity “drops out” of the circuit. The voltage then divides evenly across the
two 100-Ω resistors.
(a)
𝑅𝐿 (Ω)
𝐼𝐿 (m A)
𝐼𝑍 (m A)
𝐼𝑇 = 𝐼𝐿 + 𝐼𝑍
No Load
10 k
4.7 k
2.2 k
1k
500
100
(b)
𝑉𝑅𝑆
𝑉𝑍
𝑉𝑇 = 𝑉𝑅𝑆 +
𝑉𝑍
Observations:
Results and Computations:
Fill-in Questions:
1. With no load resistor connected at points A and B, Iz _____________________ IT
2. When IL increases, Iz ___________________________________.
3. When IL decreases, Iz ___________________________________.
4. Voltage VRS should always remain nearly ________________________.
5. Voltage VZ should always remain nearly ________________________.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 11
USING ZENER DIODES AS VOLTAGE LIMITERS
Introduction:
Refer to figure below and note that a Zener diode can be used to limit peak voltages,
thereby protecting other circuit that cannot withstand high voltages. In the forward-biased
condition (when the positive alternation is present), the Zener diode conducts and a +0.7-V
Drops is seen across the load resistor. In the reverse-biased condition (when the negative
alternation is presented), the Zener diode does not conduct until the voltage exceeds its
Zener voltage breakdown point (VZ) the diode then conducts, the output voltage will now be
clipped or clamped at the VZ level.
Objective:
1. To demonstrate Zener diode application as an AC voltage limiter
Apparatus/Materials:





1 19-Vpp AC source or a 6.3-V RMS Transformer
1 Oscilloscope
1 1N5231 Zener diode (5.1V) or equivalent Z1
1 100-Ω Resistor at 1.0W (R L )
1 Breadboard for constructing circuit
Procedure:
1. Construct the circuit shown below.
2.
3.
4.
5.
6.
7.
Connect the oscilloscope across VOUT and ground.
Verify the peak-to-peak voltage output wave form as seen in the figure.
Turn off the 18-Vpp input voltage (Vin )
Turn the Zener diode around in the circuit.
Apply the 18-Vpp input in the voltage (Vin )
Draw the output voltage waveform below and indicate its voltage levels.
Observations:
Results and Computations:
Fill-in Questions:
1.
2.
3.
4.
The Zener diode can be used as a voltage ______________________.
In the forward biased condition, voltage drop across the Zener diode is ______________.
In the reversed biased condition, the output voltage is clamped at __________________.
When diode was turned around in the circuit, the highest voltage output was
_____________________.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 12
TESTING BIPOLAR TRANSISTORS
Introduction:
For ohmmeter testing purpose, an NPN transistor is similar to two diodes back to back,
as shown in figure 12b. there exists two PN junctions, base-emitter and base collector. When
each of these junctions is forward biased, the positive lead of the ohmmeter must be
connected to P material, and the negative lead to the negative N material (Figure 12c). there
should be low resistance reading when these junctions are reverse biased, positive lead to N
material and negative lead to P material (figure 12d).
The PNP transistor can be tested with a similar method, except that the diodes are
face to face as shown in figure 12e. this simple test determines if the transistor is shorted or
open on a go (no problems)/no go (it has problems) basis.
Objective:
1. To demonstrate a practical go/no go method of testing bipolar transistors with an
ohmmeter.
Material Needed:


Standard or digital ohmmeter
1 or several bipolar transistors including both type, NPN and PNP
Procedure:
1. Set the ohmmeter to the midrange scale.
2. Refer to figure 12c to connect the ohmmeter to an NPN transistor for each junction and
record the reading in the indicated ohmmeter circles as high or low.
3. Refer to figure 12d to connect the ohmmeter to the NPN transistor for each junction and
record the readings in the indicated ohmmeter circles as high or low.
4. Using a PNP transistor, perform the same procedure as in steps 1 through 3, while
referring to figure 12f and g.
Figure 12: testing bipolar transistors with an ohmmeter; (b) NPN diode equivalent circuit; (c)
and; (d) NPN ohmmeter connections; € PNP diode equivalent circuit; (f) and; (g) PNP
ohmmeter connections.
Observation:
Conclusion:
Fill-in Questions:
1. A forward-biased PN junction on a good bipolar transistor has _______________
resistance.
2. A reverse-biased PN junction on a good bipolar transistor has _________________
resistance.
3. A forward-biased PN junction with a high ohmmeter reading indicates that the
transistor is ________________.
4. A reverse-biased PN junction with a low ohmmeter reading indicates that the
transistor is ________________.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 13
BIPOLAR TRANSISTOR AS A SWITCH
Introduction:
Refer to figure 13a and note that when switch S1 is in position A the emitter-base
junction is reverse biased (VB = 0V), the transistor is not conducting (off), and the total circuit
voltage (+VCC ) will appear at the collector (VC or across collector and emitter). When S, is in
position B, the emitter base junction is forward biased (VB ≈ 0.7) the transistor is conducting
(on), and the collector voltage will be near ground potential (VC ≈ 0.2 V). the transistor is
saturated in this condition.
Objective:
1. To recognize, by circuit voltage drops, whether a bipolar transistor is conducting or nonconducting when used as a switch.
Material Needed:
 1 Fixed 12-V power supply
 1 Standard or digital voltmeter
 1 2.2 kΩ resistor at 0.5 W (R L )
 1 2.2 kΩ resistor at 0.5 W (R B )
 1 2.2 kΩ resistor at 0.5 W (R L )
 1 100 kΩ resistor at 0.5 W (R A )
 1 2N222 transistor or equivalent
 1 Double – pole single – throw (DPST) switch (S1)
 1 breadboard for constructing circuit
Procedure:
1. Construct the circuit shown in FIG. 13a
2. Make sure that 𝑆1 is in the position A.
3. Measure 𝑉𝐵 and record the value in the data table (next to A)
4. Measure 𝑉𝐶 and record the value in the data table (in the same row)
5. Indicate in the data table if the transistor is on or off (in the same row)
6. Move 𝑆1 to position B
7. Measure 𝑉𝐵 and record the value in the data table (next to B)
8. Measure 𝑉𝐶 and record the value in the data table (in the same row)
9. Indicate in the data table if the transistor is on or off (in the same row)
10. Calculate the approximate 𝐼𝑐 from the formula.
IC =
𝑉𝑅𝐿
𝑅𝐿
=
𝑉𝐶𝐶−𝑉𝐶 (𝑜𝑛)
𝑅𝐿
(a)
𝑆1 position
𝑉𝐵
𝑉𝐶
Condition of Transistor
( ON or OFF)
A
B
(b)
Figure 13: BIPOLAR TRANSISTOR used as a switch (a) Schematic Diagram; (b) Switch Condition
Table.
11. Record 𝐼𝐶 here:
Observations:
Conclusion:
Fill-in Questions:
1. When the transistor is cut off (not conducting) the voltage at the collector ( 𝑉𝐶 ) will equal
_________________________.
2. When the voltage between base and emitter (𝑉𝐵 is 0V, the transistor is not ___________.
3. When 𝑉𝐶 is near ground potential, the transistor is __________________________.
4. If an NPN silicon transistor is in saturation, the voltage drop from base to emitter will be
about _______________________________V.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 14
BIPOLOAR TRANSISITOR AS A VARIABLE RESISTOR
Introduction:
Refer to figure 14a and note that resistor R A is changeable to produce different values of IB .
This in turn creates various values of IC and in effect resistance (R X ) of the transistor. The
supply voltage + VCC should be kept constant for each change of R A . Approximate values IB
and R X are found from the formulas given in the data table of figure 14b. the dc beta is also
approximate in the last column.
Objective:
1. To demonstrate how IB directly controls IC in a bipolar transistor and how the resistance
of the transistor varies inversely.
Materials Needed:











1 Fixed 12-V power supply
1 Standard or digital ammeter
1 standard or digital voltmeter
1 2N222 transistor or equivalent
1 1-MΩ resistor or equivalent
1 470 - kΩ resistor at 0.5 W
1 220 - kΩ resistor at 0.5 W
1 100 - kΩ resistor at 0.5 W
1 47 - kΩ resistor at 0.5 W
1 22 - kΩ resistor at 0.5 W
1 breadboard for constructing circuit.
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Construct the circuit shown in figure 14a, leaving point A and B open.
Place the 1-MΩ resistor at points A &B.
Make sure that + VCC is held at +6 V with each change of R A .
Measure the value of IC and record on the data table.
Calculate IB from the formula IS ≈ +VCC /R A and record the result in the data table.
Calculate R X from the formula R X = +VCC / IC and record the result in the data table.
Calculate Bdc from the formula Bdc = IC / IB and record the result in the data table.
Repeat steps 2 through 7 for the remaining R A values given in the data table.
(a)
𝑅𝐴 Ω
1M
4.7K
2.2K
100K
47K
22K
𝐼𝐶 μA
𝐼𝐵 = +𝑉𝐶𝐶 / 𝑅𝐴 μA
𝑅𝑋 = +𝑉𝐶𝐶 /𝐼𝐶 Ω
β𝑑𝑐 = IC/ 𝐼𝐵
(b)
Figure 14: BIPOLAR TRANSISTOR USED AS A VARIABLE RESISTOR (a) Schematic; (b) Data Table.
Observation:
Conclusion:
Fill-in Questions:
1. When 𝐼𝐵 increases, __________________increases.
2. When 𝐼𝐶 increases, ___________________increases.
3. The transistor is said to be in the active region when it operates as a _____
resistance.
4. Amplification takes place in the ____________________ region.
5. The beta of the transistor is not ______________________, but may vary considerably.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 15
TESTING JFETS
Introduction:
For ohmmeter testing purposes, the N-channel JFET is similar to a diode with its
cathode connected to the middle of a resistor, as shown in Fig. 15b. The ohmic resistance of
the channel should be about the same regardless of the polarity of the ohmmeter lead
connection from source to drain. With the positive lead on the gate, there should be a lowresistance reading when the negative lead is on the gate and the positive lead is placed on
the source or drain. The reading should be infinite when the negative lead is on the gate and
the positive lead is placed on the source or drain. The same procedures are used for a pchannel JFET, except that the diode’s anode is connected to the resistor and the ohmmeter
polarities are preserved.
Objective:
1. To demonstrate a practical go/no go method of testing JFETs with an ohmmeter. This is
called go/no go test.
Materials Needed:
 A standard or digital voltmeter
 One or several JFET’s, including both N and P-channels types
Procedure:
1. Set the ohmmeter to the midrange scale.
2. Refer to Figure 15c to connect the ohmmeter to a N-channel JFET and record the readings
in the ohmmeter circles indicated.
3. Refer to Figure 15d to connect the ohmmeter to a N-channel JFET and record the readings
in the ohmmeter circles indicated.
4. Using a P-channel JFET, perform the same procedures to figure 15f and g.
(a)
Observations:
Conclusion:
Fill-in Questions:
1. For an N-channel JFET, with the positive lead on the gate and the negative lead on the
source, the ohmmeter should read _____________________, compared to
_______________ or ________________ when the leads are reversed.
2. For a P-channel JFET, with the positive lead on the gate and the negative lead on the drain,
the ohmmeter should read ___________ or __________, compared to ______________
when the leads are reserved.
3. If the positive lead is placed in the drain and the negative lead is placed on the source and
the ohmmeter reads infinity, the JFET is _______________.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 16
OPERATION OF A JFET
Introduction:
Refer to Figure 16a and note that, when switch S1 is in the position A1 VCS =0V and
the JFET is on or conducting the voltage at the drain should be very low when the switch is
placed in position B, VCS =3V and the JFET is off or not conducting, the voltage at the drain
should be the same as +VDD .
Objective:
1. To show how to turn off a JFET and how to recognize these conditions by the voltage
prevent at the drain.
Materials Needed:
 1 Adjustable dual ± 12-V power supply
 1 Standard or digital voltmeter
 1 10-kΩ resistor at 0.5 W (R D )
 1- MΩ resistor at 0.5 (R G )
 1 2N3823 JFET or equivalent
 1 Single-pole double-throw (SPDT) switch (S1 )
 1 Breadboard for constructing circuit
Procedure:
1. Construct the circuit shown in figure 16a.
2. Make sure the 𝑆1 is in position A.
3. Measure 𝑉𝐺 and record the value in the data table next to A in figure 16b.
4. Measure 𝑉𝐷 and record the value in the data table (in the same row)
5. Indicate in the data table if the JFET is in on or off (in the same row)
6. Moves 𝑆1 to position B.
7. Measure 𝑉𝐺 and record the value in the data table next to B (in the second row).
8. Measure 𝑉𝐷 and record the value in the data table (in the same row)
9. Indicate in the data table in the JFET is in on or off (in the same row)
10. Calculate the approximate 𝐼𝐷 from the formula
𝑉
+𝑉 −𝑉 (𝑜𝑛)
𝐼𝐷 = 𝑅𝑅𝐷 = 𝐷𝐷 𝑅 𝐷
𝐷
𝐷
11. Record 𝐼𝐷 here: ________________________________
Figure 16a
𝑆1 position
𝑉𝐺
𝑉𝐷
Condition of
JFET (on or off)
A
B
Figure 16b
Observation:
Conclusion:
Fill-in Questions:
1. When JFET is conducting heavily, the voltage at the drain will be _______________.
2. When VGS = OV, the JFET is ____________________.
3. When the JFET is not conducting, the voltage at the drain will equal _____________.
Student’s Name:
Group:
Instructor’s Name:
Date:
EXPERIMENT NO. 17
CURRENT – VOLTAGE CHARACTERISTICS
Introduction:
This experiment requires a variable positive voltage for VDS and a negative voltage
for VGS . First, VGS is set to a given value; then VDS is increased to various voltages give in the
data table of figure 17b, as ID is measured and recorded. This procedure is repeated for
various values of VGS until the data table is complete. The data are then plotted in the graph
to give a more visual indication of the relationship of VGS and VDS to that of ID .
Objectives:
1. To demonstrate how the VGS has some more influence over ID than the voltage across
the drain source (VDS ); and
2. To construct a graph of output characteristics curves to understand better the operation
of a JFET.
Materials Needed:






1 Adjustable dual ± 12-V power supply
1 standard or digital voltmeter
1 standard or digital ohmmeter
1 2N3823 N-channel JFET or equivalent
1 10-k potentiometer
1 Breadboard for constructing circuit
Procedures:
1. Construct the circuit shown in figure 17a.
2. Adjust R G for A VGS reading of 0V.
3. Adjust the positive power supply for a VDS of 1V.
4. Measure ID and record the value in the proper location of the data table.
5. Increase VDS to the next value in the data table.
6. Measure ID and record the value in the proper location of the data table.
7. Repeat steps 5 and 6 for the VDS value given in the data table up to +20V.
8. Adjust the variable positive power supply to 0V.
9. Adjust R G for the next value of VGS given in the data table.
10. Repeat steps 3 to 8 to complete the readings for ID .
11. Continue this procedure of increasing VGS and VDS while measuring and recording ID for
the values given in the data table.
12. When the data table is complete, arranged the data on the graph to construct the I-V
characteristics curves (refer to figure 17c).
a. ) using the first row of data, find the intersection of VDS and the recorded ID and
mark dots horizontally along the graph. Next connect the dots with a straight line.
At the end of line to the right, record the value of VGS for the line of data.
b. ) follow the same method until all the rows of data are displayed on the graph.
Figure 17a
𝑉𝐺𝑆
𝑉𝐷𝑆
0
1
2
3
0
1.5
1.0
1.5
2.0
2.5
3.0
(17b)
4
5
10
15
20
𝐼𝐷 (mA)
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
(17c)
Observation:
Conclusion:
Fill-in Questions:
When bias voltage 𝑉𝐺𝑆 increases, there is a __________________________ in 𝐼𝐷 .
When 𝑉𝐷𝑆 increase, there is little or no increase change in __________________.
Gate voltage has more control of _____________ than does ______________.
The graph shows the relationship of ________________, _________________ and
__________________.
5. From the graph, when 𝑉𝐺𝑆 = -1.5V and 𝑉𝐷𝑆 = +10V, then 𝐼𝐷 = ________________mA.
1.
2.
3.
4.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0