IC Regulated DC Power Supply Semester 5
Objectives
➢ Design and study of a 9V IC-regulated DC power supply using IC 7809
Apparatus/ Components Required:
★ IC-7809: 1 ★ Digital Multimeters: 3
★ Step-down transformer (230V-9V): 1 ★ Bread Board: 1
★ p-n diodes: 4 (or) W10 bridge: 1 ★ Connecting Wires
★ Capacitors
Theory:
AC and DC: Current is direct if it always flows in the same direction, whereas
alternating current periodically changes direction.
Rectification: A rectifier is an electronic circuit that converts the alternating
current (AC) into direct current (DC). The conversion of alternating current into direct
current is known as rectification. The rectifier consists of semiconductor diodes that
perform the rectification.
Regulation: Voltage Regulation is maintaining the O/P voltage of the supply
constant in the face of variations in
1. Line (supply) voltage
2. Load (current)
3. Temperature; remember that semiconductor components are sensitive to
temperature
Think! why AC to DC conversion is required 🤔
📖 IC 7809 pin configuration:
7809 Voltage regulator is a
self-contained fixed linear voltage
regulator integrated circuit. The IC
belongs to the 78xx voltage regulator
family, commonly used as the regulated
power supply in electronic circuits. The
last two digits of 7809 indicate the
output voltage. The 7809 regulator line
is a positive voltage regulator, and the
7809 voltage regulator IC generates the
voltage, which is positive concerning the common ground. The voltage regulator 7809 is
combined with its corresponding 78xx family IC. The 7809 voltage regulators operate at
their optimal capability if the input voltage is at least 2.5 volts greater than the output
IISER-TIRUPATI 1
IC Regulated DC Power Supply Semester 5
voltage and the current is 1 or 1.5A more. The IC 7809 has 3 pins, pin-1 is a positive input,
pin-3 is a positive output, and pin-2 is a negative common ground between the input and
output voltage. When using the 7809 regulator setup, you need to take care that the
current through the voltage regulator 7809 does not exceed the capacity (Voltage:11-35V
and Current: 1-1.5A) or else it may blow off. You also have to be careful with the
connection you are making with the voltage supply. Reverse polarity does get the IC to
heat up quickly; you can also use a p-n junction diode to prevent such a condition. You
can use the capacitors to reduce the voltage fluctuations in the circuit and maintain the
constant voltage across the input and output stages of the circuit.
Think! why regulation is required 🤔
📖 W10 bridge rectifier equivalent circuit:
W10 is a single-phase and full-wave bridge rectifier IC with 1000V and 1.5A
voltage and current rating, respectively.
Circuit Diagram:
IISER-TIRUPATI 2
IC Regulated DC Power Supply Semester 5
Description:
The circuit diagram of the 9V regulator using the famous 7809 IC as shown above.
The 7809 is a 9V voltage regulator IC with an internal current limit, safe area protection,
thermal protection, etc. A step-down transformer will step- down the voltage from 230V
AC mains to the 9V level. The transformer's output is given as an input to the rectifier
circuit. A full wave rectifier (a bridge rectifier or W10 bridge) converts the AC supply's
half cycles to unidirectional pulsating DC. The rectified voltage from the rectifier is a
pulsating DC voltage with a very high ripple content. But we want something else; we
want a pure ripple-free DC waveform. Hence, different filters, such as capacitor filter, LC
filter, Choke input filter and π type filter, can be used. The figure above shows a
capacitor filter connected across the output of the rectifier. The output voltage or current
can change or fluctuate when there is a change in the input from AC mains due to the
change in load current at the output of the regulated power supply or other factors like
temperature changes. This problem can be eliminated by using a regulator. A regulator
will maintain the output constant even when changes at the input or any other changes
occur. Here, IC 7809 is used as the voltage regulator, which gives regulated 9V DC at the
output.
Procedure:
● Make the connections as per the circuit diagram shown above.
● Initially, construct the bridge rectifier using ordinary p-n diodes.
● Measure the ac voltage across the secondary winding of the transformer.
● Measure the ac and dc output of the full-wave rectifier without a filter circuit and
calculate the ripple factor 𝛄 = Vac/Vdc
● Measure the ac and dc voltage across the capacitor ‘C’ and calculate the ripple
factor 𝛄 = Vac/Vdc
● Apply unregulated dc voltage to the IC 7809 and measure the regulated dc output
voltage using a digital multimeter.
● Use 0.01 µF for the bypass capacitor Cb.
● Perform the experiment by changing suggested capacitor values i.e., 3.3, 4.7, 10,
50, 100, 220,470, 1000 and 2200 µF and calculate the ripple factor for each value
of the capacitance.
● Insert W10 bridge by replacing ordinary diodes and repeat the same procedure to
verify the regulated output.
IISER-TIRUPATI 3
IC Regulated DC Power Supply Semester 5
Observations:
Table-1: Calculation of ripple factor without capacitor filter.
Output voltage Output voltage
across the across the rectifier circuit Ripple Factor
S. No
transformer (without filter) 𝛄 = Vac/Vdc
Vac (V) Vac (V) Vdc (V)
1.
2.
3.
Avg.:
Table-2: Calculation of ripple factor with capacitor filter.
Voltage across the DC output
Capacitor capacitor (C) Ripple factor across the IC
S. No
(µF) 𝛄 = Vac/Vdc 7809
Vac (V) Vdc (V) Vo (V)
1.
2.
3.
4.
5.
Think! why ripple factor decreases as capacitance increases 🤔
IISER-TIRUPATI 4
IC Regulated DC Power Supply Semester 5
Precautions:
● Carefully examine the circuit diagram and note all the components and how they
are connected. Pay attention to the symbols used for each component.
● Collect all the necessary components and ensure they are in good working
condition. Clean the terminals of the components and connecting wires.
● Follow the connections shown in the diagram, using appropriate wires to connect
the terminals of each component.
● Pay close attention to polarity markings and ensure the components are
connected in the correct orientation.
● Use a wire stripper to remove insulation from the ends of the wires before
connecting them.
● Before applying power, carefully inspect all the connections to ensure they are
correct and there are no loose wires or shorts.
● If using a power supply, set the voltage and current limits according to the
diagram.
● If the circuit is designed to have a specific behavior (e.g., a light bulb glowing, a
motor turning), observe whether it is functioning as expected.
● If the circuit is not working as expected, carefully re-examine the connections,
component values, and polarity. Use a multimeter to check for voltage and current
at various points in the circuit to help identify any issues.
● Disconnect the power supply and multimeter once your experiment is complete.
However, ensure that the configured parameters are reduced before shutting off
the power supply.
● Handle the step down transformer carefully as it involves live currents.
● Connect the p-n diodes carefully while making bridge rectifiers.
● Place the W10 bridge carefully and make the connections as per the signs
printed over it.
● Verify the IC 7809's pin numbers and the capacitors' polarity while connecting
the circuit.
Results & Inference:
IISER-TIRUPATI 5
IC Regulated DC Power Supply Semester 5
References:
● Books/articles:
1. Electronic Principles: A. P. Malvino (1999) 6th edition McGraw-Hill.
2. The Art of Electronics: P. Horowitz and W. Hill (1989) 2nd edition Cambridge
University Press
3. Electronic Devices and Circuits: R. Boylestad and L. Nashelsky (2015) 11th edition
Pearson Education
4. Digital Design: M. M. Mano and M.D. Ciletti (1989) 4th edition Pearson Education
5. Digital Fundamentals, Thomas L Floyd (2014) 11th Edition Pearson
📖
6. Principles of electronics V.K.Metha, Rohit Metha (1980) 4th edition.
7. Digital Multimeter datasheet
Note:
● Strictly follow the precautions mentioned in the safety guidelines 📖.
Sample circuit and Result:
IISER-TIRUPATI 6
