Introduction

Welcome! In this guide, we will focus on designing a 5V power supply. We will walk through the design process, covering essential calculations and explaining each step in detail. The goal of this article is to share the necessary know-how, ensuring that by the end of the tutorial, you will have the skills to design a power supply tailored to your specifications and requirements. This project guide will walk you through each design stage, including the mathematics behind the design. For example, if we include a capacitor in the schematic, we will explain why it is there, its purpose, and how we selected its value.

Project Requirements

By the end of this guide, you will be able to:

• Design a 5V DC output power supply with an input of 220V AC, a current output of 250mA, and a ripple factor of 3%.
• Ensure the power supply includes over-current and over-voltage protection features.
• Implement reverse-bias protection in the design.
• Achieve load and line voltage regulation within a 3% tolerance.

Let’s begin with a complete design guide.

Power Supply Universal Block Diagram

Generally, a power supply block diagram consists of the following components:

• The Input Transformer
• The Rectifier Circuit
• The Filter
• The Voltage Regulator

Let’s take a closer look at the block diagram and examine what each component does before diving into the actual design.

Figure 1: General Power Supply Block Diagram

Each section of the block diagram has a specific role, and we need to understand these functions to know why they are necessary.

Input Transformer

Transformers are responsible for stepping up or stepping down the voltage, in accordance with the principle of energy conservation.

In our design, we will use a step-down transformer to reduce the input voltage from 220V (depending on your country) to a value closer to 5V, which is the target output for our project.

The Rectifier Circuit

The voltage from the transformer is AC, and to convert it to DC, we need a rectifier circuit. Without this, achieving a 5V DC output would be impossible.

• Rectifier circuits are available as integrated circuit packages, but we can also design a full-wave rectifier using four diodes.
• While half-wave and full-wave rectifiers exist, our design will focus on the full-wave rectifier.

Voltage Filter

The rectifier converts AC to DC, but the output is not pure DC. Instead, it is pulsating DC.

Pulsating DC is unsuitable for powering sensitive electronic devices because it is noisy and contains ripples.

A filter is used to smooth out these pulses and ripples, making the voltage compatible with the voltage regulator.

For optimal voltage regulation, the filter should reduce ripple to below 10%. The best filter for this project is a capacitor, which stores and releases charge.

Voltage Regulator

A voltage regulator ensures a constant output voltage, regardless of changes in load or line voltage.

Figure 2 below illustrates the behavior of the components in the block diagram from Figure 1.

Figure 2: Power Supply Block Diagram and Graphical Analysis

5V DC Linear Power Supply Circuit Diagram

Figure 3: 5V DC Power Supply Schematic Using KiCAD EDA

Figure 3 shows the circuit diagram for our power supply design. The main power input is 220V RMS at 50Hz, though this can vary depending on your country’s specifications. The circuit includes a fuse for protection, a transformer to step down the voltage, a rectifier, a filter capacitor, an LED indicator, and a voltage regulator IC.

This circuit was designed and simulated using KiCAD EDA, an open-source software ideal for both professional and educational PCB design.

Next, let’s proceed to the step-by-step design of the power supply.

Power Supply Step-by-Step Design Method

At this stage, we will design each section of the power supply and combine them to form the final design.

Step 1: Voltage Regulator IC

Based on the datasheet for the voltage regulator IC, a 0.1uF capacitor is connected at the output for protection against load changes and transient voltage. At the input, a 0.33uF capacitor is used to filter out ripples.

Step 2: Transformer

The transformer’s current rating is 1A, as per the datasheet for the regulator IC.

Step 3: Rectifier Circuit Diodes

Using the transformer’s secondary voltage, we can calculate the required capacitor voltage rating. As a rule of thumb, the capacitor’s voltage rating should be at least 20% higher than the transformer’s secondary voltage.

Let’s calculate the capacitor’s value mathematically:

Since we are using a full-wave rectifier, the ripple frequency will be 120Hz.

From the table of standard capacitor values, we find that 397uF is not available. Therefore, we will select the nearest standard value of 470uF for the filter capacitor.

Step 5: Securing the Power Supply

All electronic designs include protective features to prevent damage. Our circuit will incorporate an input fuse to protect against overloading.

Since the maximum current for our power supply is 1A, the fuse should be rated for 1A or less.

3D Output of the 5V Power Supply Using KiCAD

After completing the circuit design and calculations for component ratings, here is the 3D view of the 5V power supply:

Figure 6: 3D Design Output of the 5V Power Supply

Summary

If you’re passionate about electronics, designing your own power supply system is an excellent place to start. It’s a great way to learn about electronic design, understand the function of different components, and develop hands-on experience. Once you’ve completed your design, you can manufacture PCBs through services like WellCircuits and test your prototypes to ensure you’ve met your project’s goals.

 

 

 

 

If you have any questions about PCBs or PCBA, feel free to contact me at info@wellcircuits.com.