School of Engineering Sciences
Department of Computer Engineering
Edward Kakra Ankrah 22382302
Asante Gabriel Kwaku 22268986
Sekyere Kofi Bempong 22403781
Manford Kelvin Oppong 22396566
Jerrold Xornam Kyekye 22396551
DESIGN AND IMPLEMENTATION OF A 5V
REGULATED DC POWER SUPPLY FOR CELL
PHONE CHARGING USING A BRIDGE
RECTIFIER
ABSTRACT
This report presents the design and analysis of a DC power supply that converts alternating current
(AC) to direct current (DC) using a bridge rectifier configuration. The system utilizes a four-diode
full-wave rectifier, commonly referred to as a "Wheatstone bridge" in informal contexts, to efficiently
rectify AC input into a pulsating DC output. The voltage is then smoothed by a capacitor and further
stabilized by a voltage regulator. This project demonstrates fundamental principles of powering
electronic devices such as phones and lays the groundwork for more advanced regulated power supply
systems.
I. INTRODUCTION
This report explores the design, construction, and analysis of a rectification circuit aimed at
converting alternating current (AC) into direct current (DC). The circuit consists of key components
including four diodes arranged in a full-wave bridge configuration, a transistor, a capacitor, a resistor,
and a light-emitting diode (LED). Each component plays a specific role in ensuring effective
rectification and stable DC output. The process of converting AC to DC is fundamental in electronics,
as most electronic devices require a steady DC supply to operate. AC, which periodically reverses
direction, is the standard form of electrical power distributed through mains systems due to its ease of
generation and transmission over long distances [1]. However, many electronic circuits especially
those involving digital logic, microcontrollers, and LEDs require a unidirectional, steady voltage.
Rectification is the initial step in the AC-DC conversion process. In this circuit, four diodes form a
full-wave bridge rectifier, enabling both halves of the AC input to be used, effectively doubling the
frequency of the resulting pulsating DC. A capacitor is connected in parallel with the load to stabilize
the output voltage by storing energy during voltage peaks and discharging during dips, thereby
minimizing ripple and producing a steadier DC output [2]. The transistor serves as an amplification or
switching element in the circuit. In this context, it may be used to regulate or stabilize the output
current, buffer the rectified voltage, or enhance the circuit’s ability to drive the LED efficiently. A
current-limiting resistor is included in series with the LED to prevent excessive current from
damaging it. The LED acts as a visual indicator, confirming the presence of DC voltage at the output.
Overall, this rectification circuit not only demonstrates the theoretical principles of AC to DC
conversion but also integrates practical elements to ensure a stable and functional DC output. The
following sections will detail the circuit design, component selection, working principle, and observed
results during testing.
II. LITERATURE REVIEW
This section contains a detailed review of existing related literature. It considered topics of interest
such as DC power supplies, Diodes, Capacitors, Transformers, Cell phone charging and voltage
regulators, which are paramount to the understanding of the development of the electronic circuits.
DC power supplies play a crucial role in the development and operation of electronic circuits. Similar
to their counterparts Alternating Current (AC), they transfer electrical energy from one point to
another. However, unlike AC. DC flows in one direction and has a constant electrical energy [3]. DC
usage in embedded systems is very critical to its functionality. According to Wang[4] DC, especially
low voltage DC has a higher efficiency in home appliances and complies better to it.
Diodes are semiconductor devices that allow current to flow in one direction, making them crucial for
regulating the behaviour of electrical circuits. The fundamental diode consists of a p-n junction,
establishing a barrier that permits current flow just when forward-biased. The functioning of a diode
relies on the dynamics of charge carriers at the p-n junction. In a forward-biased state, the potential
barrier diminishes, facilitating current flow. In reverse bias, the barrier height grows, obstructing
current flow until breakdown transpires.
Cell phone chargers, namely USB Type A chargers, consume 5-10 watts of power to charge a
smartphone. USB Type A, akin to Type B, can be placed into the port in just one orientation. The
USB icon located at the top indicates the correct upward orientation. The energy consumption of type
A chargers often varies between 5 and 10 kWh. Micro and mini-USB, with the former regarded as the
most prevalent charger type historically, have numerous applications, including flash drives, cameras,
and keyboards. Similar to its widely used equivalent, USB Type A, it is designed to connect on only
one side. USB Type-C chargers represent the latest advancement in charging technology for phones
and other gadgets. The reversible connectors are transformative, as they eliminate the need to consider
a certain orientation for use. Low wattage chargers possess a power output ranging from 5 to 10 watts;
these chargers are effective for prolonging the duration of phone usage and do not contribute to
overheating issues. The sole disadvantage is the prolonged duration required for a complete charge.[5]
According to Texas Instruments [6], linear voltage regulators like the 78XX series are commonly used
in low-power applications to provide a stable output voltage. These regulators are easy to implement
and offer low output noise, making them ideal for simple DC power supply circuits. The 78xx series,
also known as LM78xx, consists of fixed linear voltage regulator ICs commonly used in electronic
circuits. These regulators are affordable and easy to use, providing stable output voltages. Each IC in
the series is identified by a two-digit number indicating its output voltage, such as 7805 for 5V or
7812 for 12V. The 78xx family provides positive voltages, while the complementary 79xx series
offers negative voltage regulators. These ICs typically support input voltages up to 35–40V and can
deliver 1 to 1.5 amps of current. They are commonly found in TO220 packages but also come in other
form factors[7].
III. SYSTEM DESIGN
Fig 1
The circuit diagram as shown in Fig 1 was used to design the physical implementation. The design of
the DC power supply circuit relies on the conversion of AC voltage, by rectification, to a stable DC
output for supply to electronic components. The system consists of a step-down transformer, a set of
four diodes for rectification, a smoothing capacitor, a voltage regulator, and a load with an indicator
LED. The components of the circuit were: a transformer, which steps down high AC voltage to a low
AC voltage suitable for rectification; a rectifier (D1-D4), which converts AC voltage to pulsating DC
voltage using four diodes in a full-wave bridge circuit; a smoothing capacitor (C1), which reduces
voltage fluctuations and causes a smoother DC output; a voltage regulator (U1), which provides a
constant 5V DC output regardless of input variations; a resistor (R1), which limits the current flowing
to the LED, thereby safeguarding it from damage; and an LED (LED1), which serves as a power
indicator.
IV. SYSTEM IMPLEMENTATION AND TESTING
Implementation
• The circuit was first assembled on a breadboard for testing.
• A transformer (XFMR1) steps down AC mains voltage to a lower AC voltage.
• The four diodes (1N4148) were connected to form a bridge rectifier.
• The bridge rectifier was wired across the secondary output of the transformer.
• A 1000µF capacitor (C1) was connected across the output of the rectifier to smooth the
DC.
• A 7805-voltage regulator (U1) was connected to regulate the DC to 5V.
• An LED (LED1) with a 1kΩ resistor (R1) was connected in parallel to the regulator's
output for power indication.
• All connections were inspected to ensure proper wiring and avoid short circuits.
• After successful breadboard testing, all components were soldered onto a PCB.
• The power was tapped to charge a phone
Testing
The testing phase involved verifying the operation of each stage to ensure the desired output was
achieved.
LED Functionality Check: The LED indicator was tested to ensure that it functioned well as a power-
on indicator.
Resistor and Capacitor Value Verification: The resistance and capacitance were measured using an
oscilloscope to ensure that they conform to their said values.
Rectification Test: The bridge rectifier output was observed using an oscilloscope to ensure the AC-DC
conversion.
Voltage Regulation Analysis: The output of the voltage regulator was checked to ensure that a stable
5V DC supply was maintained.
V. RESULTS AND ANALYSIS
Time (s) Step-Down Regulated Voltage
Voltage (V) (V)
0 12.0488 5
1 12.2152 5
2 12.102 5
3 11.8934 5
4 11.925 5
5 11.9756 5
6 12.364 5
7 12.393 5
8 12.046 5
The DC power supply circuit was effectively executed and evaluated. The results from the
testing phase were documented for a duration of 10 seconds. The step-down transformer
reliably decreased the AC mains voltage to an average of about 12V, with minor fluctuations
between 11.8V and 12.4V resulting from inherent variances in the input supply and
component tolerances.
The voltage regulator (7805) consistently provided a stable 5V DC output over the testing
period, validating its function in voltage stabilization despite slight variations in the input.
This continuous regulation underscores the dependability of the 7805 regulators in low-power
applications, including phone charging circuits and microcontroller-based devices.
The LED indicator remained illuminated throughout the test, indicating a persistent output
voltage.
The circuit was employed in a practical test to charge a mobile phone over a USB connection.
The phone started the charging process, indicating that the circuit provided sufficient power
and current. During the charging interval, the regulated voltage remained constant at 5.0V,
demonstrating that the circuit sustained output stability despite the load.
VI. CONCLUSION AND RECOMMENDATIONS
Conclusion
The development of a DC power supply from an AC source using fundamental electronic components
has been successfully demonstrated in this project. The circuit built around a step-down transformer,
smoothing capacitor, voltage regulator, and an indicator LED reliably converted erratic alternating
current into a steady 5V DC output, mirroring the kind of stable power needed for everyday devices
like phone chargers or microcontrollers.
Testing revealed how each component earned its place: the full-wave rectifier squeezed every bit of
efficiency from the AC input, the capacitor tamed voltage ripples, and the regulator locked in that
crucial 5V output. Even the humble LED, with its current-limiting resistor, played a starring role as a
visual "all systems go" signal.
The literature review added depth, showing how this work ties into real-world needs from the
efficiency of DC in smart homes to the engineering behind modern charging tech. It’s a reminder that
even simple circuits underpin technologies we rely on daily.
Beyond checking the project’s goals off the list, this hands-on process deepened my understanding of
electronics fundamentals. The leap from textbook diagrams to a working circuit was both challenging
and rewarding. Future tweaks like adding adjustable voltage or boosting efficiency could make this
design even more versatile.
In the end, this lab wasn’t just about building a power supply; it was about connecting theory to
practice, one component at a time.
Recommendation
Ripple Voltage: Despite the smoothing capacitor, some ripple may persist in the output, which
could affect sensitive electronic components requiring ultra-stable DC voltage. To solve this, add a
second-stage LC filter or use a larger capacitor to further reduce ripple voltage for more sensitive
applications.
Also, Component Tolerance: Variations in component values (e.g., capacitor aging or resistor
tolerance) could lead to deviations in output performance over time. To solve this, use precision
components, e.g., 1% resistors and temperature-stable parts. Add parallel capacitors and trimpots for
adjustability. Pre-test components and simulate worst-case scenarios to ensure stable output.
VII. REFERENCES
[1] L. N. Titova and V. A. Sergeev, “Methodological problems of replacing low-voltage AC
networks with DC networks,” IOP Conf Ser Mater Sci Eng, vol. 1035, no. 1, p. 012041, Jan.
2021, doi: 10.1088/1757-899X/1035/1/012041.
[2] V. Mahadeva Iyer and V. John, “Low‐frequency dc bus ripple cancellation in single phase
pulse‐width modulation inverters,” IET Power Electronics, vol. 8, no. 4, pp. 497–506, Apr.
2015, doi: 10.1049/iet-pel.2014.0320.
[3] H. D. Young, R. A. Freedman, and A. Lewis Ford, University physics with modern physics,
13th edition. Upper Saddle River, NJ, United States of America : Pearson, 2010.
[4] S. Wang, C. Zhang, and Q. Zhao, “FPGA-Based modelling and embedded real-time simulation
of low-voltage DC distribution system with multiple DESs,” Electric Power Systems
Research, vol. 245, p. 111621, Aug. 2025, doi: 10.1016/j.epsr.2025.111621.
[5] S. Manoharan, B. Mahalakshmi, K. Ananthi, and A. Elakya, “A Review on Smartphone
Charger: Technologies and Challenges,” in 2024 5th International Conference on Intelligent
Communication Technologies and Virtual Mobile Networks (ICICV), IEEE, Mar. 2024, pp.
84–88. doi: 10.1109/ICICV62344.2024.00020.
[6] Texas Instruments, “ Linear and Switching Voltage Regulator Fundamental Part 1,” Texas
Instruments.
[7] Sandeep Kumar, “Design and Development of Head Motion Controlled Wheelchair,” Chennai,
2015.
