# Objective To familiarize with the basic features of the - DOC - DOC by aah15699

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```									                                       ELEC2103                                 EXERCISE 16

Objective:     To build, test and understand various types of power supply circuits.

PART 1: FULL WAVE BRIDGE RECTIFIER CIRCUIT

    The full wave bridge rectifier circuit is the building block of va rious types of power supply circuits. Adding a
capacitor will smooth the pulsating DC voltage. Adding a zener will regulate the DC output voltage. Adding
different types of IC regulat ors will provide a constant or adjustable DC voltage.

Multisim Circuit

1.       Using Multisim, construct the circuit shown in Fig. 1 using a 10:1 step down transformer. Vprimary is 120 VAC

2.       The diode bridge is located in the Components Toolbar → Diode → FWB → 1B4B 42.

Fig. 1

Calculations

Calculat e the following before taking any measurements:

1.       Vsec rms [ = V pri rms /turns ratio ] __________________________________________________________

2.       Vsec peak [ = Vsec rms /0.707 ] ____________________________________________________________

3.       Vload peak [ = V sec peak – 2*0.7V ] _________________________________________________________
ELEC 2103 – E X 16                                                                                                   Page 2

Vload dc ave [ = V load peak/p * 2 ] _____________________________________________________________

Measurements

1.       Connect a DC voltmeter to measure the average DC voltage across the 1 kΩ load, and complete Table 1.

2.       Connect Ch A of a scope to measure the voltage across the 1 kΩ load. Use the Grapher to get more
accurate results, and complete Table 1.

Calculat ed               Measured

PART 2: BRIDGE RECTIFIER CIRCUIT WITH A FILTER CAPACITOR

        A capacitor connected in parallel with the load, after the bridge circuit, is called a filter capacitor, because it
will smooth the pulsating DC voltage. The higher the capacitor value, the smaller the ripple voltage, and the
smoother the DC output volt age.

1.       Modify the circuit of Fig. 1 by adding a 100 μF capacitor between the bridge rectifier and the 1 kΩ load. See
Fig. 2.

Fig. 2

Calculations

th
Calculat e the ripple voltage V ripple using Paynter’s approximation method (6 ed., pg 108).
ELEC 2103 – E X 16                                                                                           Page 3

1.   Vripple [ = Iload dc ave*t/C, where Iload dc ave ≈ Iload peak, t = 1/f for full wave = 8.33 ms]

____________________________________ __________________________________________________

2.   Vload dc ave [ ≈ V load pk – Vripple/2 ] __________________________________________________________

Measurements

1.   Connect Ch A of a scope ac ross the load to measure the ripple voltage. Use the Grapher to get more
accurate results, and complete Table 1.

2.   Connect a DC voltmeter ac ross the load to measure the avera ge DC voltage. It will be higher than the result
in Table 1.

Calculat ed                 Measured
Table 2
Vripple w /100 μF

Vdc average w/100 μF

What if ?    a) If the 100 μF capacitor is replac ed with a 1000 μF capacitor, calculate the new V ripple.

________________________________________________________________________________

b) Calculate the new V load dc ave ______________________________________________________

c) Use Grapher to measure the new V ripple, and complete Table 3.

d) Use a DC voltmeter to measure the new V dc ave, and complete Table 3.

Calculat ed                 Measured
Table 3
Vripple w /1000 μF

Vdc average w/1000 μF
ELEC 2103 – E X 16                                                                                               Page 4

PART 3: BRIDGE RECTIFIER CIRCUIT WITH A FILTER CAPACITOR AND A ZENER DIODE

    A zener diode is placed bet ween the capacitor and the load to regulate the voltage across the load.

Multisim Circuit

1.       Modify the circuit of Fig. 2 by adding a 1N751A Zener diode and a series resistor between the capacitor and
the 1 kΩ load. Use a 1000 μF capacitor. See Fig. 3.

2.       From the spec sheet for the 1N751A Zener diode, Vz = _______________, I ZT = _______________

3.       Calculat e Rseries [ = V dc ave @ capacitor – Vz / Iseries , where Iseries = Iload + IZ operating ]

______________________________________________________________________________________

Fig. 3

Measurements

1.       Connect a DC voltmeter ac ross the load to measure the regulated DC voltage and complete Table 4.

Calculat ed                 Measured
Table 4

What if ?        a) If the 1N751A Zener diode was replaced with a 1N755A Zener diode, calculate the new V dc. Verify
your result using a DC voltmeter.

________________________________________________________________________________

b) If the 1N751A was accidentally connected backwards in the circuit in Fig. 3, calculate the new V dc.
Verify your result using a DC voltmeter.

________________________________________________________________________________
ELEC 2103 – E X 16                                                                                                 Page 5

PART 4: BRIDGE RECTIFIER CIRCUIT WITH AN IC VOLTAGE REGULATOR

    A linear IC voltage regulator is an integrated circuit that will hold the output voltage from a DC power supply
relatively constant over a specified range of line and load variations.
    Eg., a 7805 regulator has a V out of 5V for a V in min/max of 7V to 25V, a 7809 regulator has a V out of 9V, a 7812
has a V out of 12V, a 7815 has a Vout of 15V.

Multisim Circuit

1.       Modify the circuit of Fig. 3 by replacing the Zener diode with a 7805 IC voltage regulator. See Fig. 4.

2.       The 7805 is located under the Component Toolbar → Misc → Voltage Regulator → LM7805CT.

Fig. 4

Measurements

1.       Connect a DC voltmeter ac ross the load to measure the regulated DC voltage and complete Table 5.

Calculat ed             Measured
Table 5

What if ?       a) If the 7805 IC regulator in the circuit if Fig 4 is replaced with a 7809, what would you ex pect the load
DC voltage to be? Complete Table 6.

________________________________________________________________________________

Calculat ed             Measured
Table 6
ELEC 2103 – E X 16                                                                                                Page 6

PART 5: BRIDGE RECTIFIER CIRCUIT WITH AN ADJUSTABLE VOLTAGE REGULATOR

    The output voltage of the LM117 voltage regulator is adjustable using a voltage divider: For the circuit shown in
Fig. 5, Vout = 1.25(R3/R2 + 1).

Calculation

1.       Suppose you want the maximum voltage output to be 10V. In the voltage divider rule, let R2 = 120 ohms, find
R3. Use a potentiometer for R3.

_________________________________________________________________________________ ______

2.       Find the minimum output voltage. Let R3 = 0 ohms, solve for V out.

_______________________________________________________________________________________

Multisim Circuit

1.       Modify the circuit of Fig. 4 by replacing the 7805 voltage regulator with the LM117 regulator. See Fig. 5.
Include a 1000 μF, 0.1 μF, and 1.0 μF capacitors as shown. Include a pot entiometer, wire it properly as
shown.

2.       The LM117 is located under the Component Toolbar → Misc → Voltage Regulator → LM117HV H. The
potentiometer is located under Virt ual Toolbar → Basic Components → Virtual Linear Potentiometer → drag it
out → double click on the potentiometer → key = Z, Resistance = 840 ohms.

Fig. 5

Measurements

1.       Connect a DC voltmeter ac ross the load to measure the adjustable DC voltage and complete Table 7.

Calculat ed             Measured
Vload dc w/ pot set to                                                                    Table 7
0
Vload dc w/ pot set to
50
Vload dc w/ pot set to
100
ELEC 2103 – E X 16                                                                                    Page 7

What if ?     If the potentiometer was changed from 840 ohms to 600 ohms, what would be the range of the
output voltage ? Complete Table 8.

_______________________________________________________________________________

Calculat ed        Measured

Vload dc w/ pot set to 0
Table 8
Vload dc w/ pot set to 50

Vload dc w/ pot set to 100
ELEC 2103 – E X 16            Print Name ________________________________________________                                 Page 6

ASSIGNMENT

1. Save your Mul tisi m file with your lastna me, followed by exercise # and question #, eg:
SMITH EX16 Q1.MS7. Sa ve each question wi th a different filena me.
2. Save all questions in one Word document eg: SMITH EX16 Q1.DOC.
3. Attach the Mul tisi m circui ts (.ms7) and the Word document (.doc) in your e-mail a t patel50@gmail.com

Q 1. a)   Using Multisim, design a full wave bridge rectifier circuit consisting of a step -down transformer with 120VAC rms primary
voltage, 8VAC rms line-to-line secondary voltage. Include a 500 μF smoothing capacitor across a 500 ohm resistive load.
b)   Use AC voltmeters to measure the voltages at the transformer primary and secondary.
c)   Use Grapher to measure Vload peak.
d)   Use a DC voltmeter and a DC ammeter to measure the load average voltage and current.
e)   Import into Word the Multisim circuit showing the AC voltages at the transformer, and the DC voltage and DC current in
f)   Import also into Word the Grapher screen with a white background showing the load voltage. Include the pop-up window
with the max y, min y details.
g)   Include in the Word document the calculated value of the ripple voltage.
h)   Include in Word a table of the calculated and measured values of all voltages and currents in steps b), c), d).

Q 2.a)  Using Multisim, design a full wave bridge rectifier circuit consisting of a step -down transformer with 120VAC rms primary
voltage, 10VAC rms line-to-line secondary voltage. Include a 2000 μF smoothing capacitor, a 1N757A zener diode across
a 1 kohm load, and a series resistor between the capacitor and the zener diode.
b) Calculate and show the appropriate size of the series resistor. Let the current in the resistor be limited to 40 mA.
c) Use AC voltmeters to measure the voltages at the transformer primary and secondary.
d) Use Grapher to measure Vload peak.
e) Use a DC voltmeter and a DC ammeter to measure the load average voltage and current.
f) Import into Word the Multisim circuit showing the AC voltages at the transformer, and the DC voltage and DC current in
g) Import also into Word the Grapher screen with a white background showing the load voltage. Include the pop -up window
with the max y, min y details.
h) Include in the Word document the calculated value of the series resistor.

Q 3. a) Using Multisim, design a full wave bridge rectifier circuit consisting of a step -down transformer with 120VAC rms primary
voltage, 12VAC rms line-to-line secondary voltage. Include a 1000 μF smoothing capacitor, a 7812 IC voltage regulator,
and a 1 μF capacitor across a 10 kohm resistive load.
b) Use a DC voltmeter and a DC ammeter to measure the load average voltage and current.
c) Import into Word the Multisim circuit showing the DC voltage and DC current in the load.

Q 4. a) Using Multisim, design a full wave bridge rectifier circuit consisting of a step -down transformer with 120VAC rms primary
voltage, 15VAC rms line-to-line secondary voltage. Include a 3000 μF smoothing capacitor, an LM117 IC voltage
regulator, a 0.1 μF capacitor and a 1 μF capacitor before and after the regulator similar to Fig. 5. Include resistor R2 =
120 ohms, and R3 = 1 kohm potentiometer with the LM117 regulator similar to Fig. 5. Include a 1 kohm resistive load.
b) Use a DC voltmeter and a DC ammeter to measure the load averag e voltage and current with the pot set to 0, 50%, 100%.
c) Import into Word the Multisim circuit, and a table of the calculated and measured values with the three pot settings.

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