1.      Introduction

A stable and adjustable DC power supply is a fundamental requirement in electronics laboratories for circuit prototyping, testing, debugging, and experimental research. Conventional laboratory-grade power supplies provide accurate regulation and protection features but are often expensive, bulky, and inaccessible to students, hobbyists, and small institutions. Consequently, there is a growing demand for compact and cost-effective alternatives that can deliver comparable performance at reduced cost [1], [2].

ATX computer power supplies are widely available due to mass production and frequent replacement cycles in desktop computers. Despite their low cost, ATX SMPS units offer high efficiency, excellent voltage regulation, and high current capability across multiple output rails such as 12V, 5V, and 3.3V [3], [6]. These characteristics make them suitable candidates for repurposing into laboratory power supplies. In particular, the 12V rail can be effectively utilized as the input to a DC–DC buck converter to generate a regulated and adjustable output voltage.

High-power buck converters are commonly used in laboratory and industrial applications due to their high efficiency, compact size, and ability to handle large currents with minimal thermal losses [4], [7]. By integrating a buck converter with an ATX power supply, a flexible and efficient variable DC power source can be realized. In addition, digital monitoring modules and protection mechanisms further improve operational safety and usability.

This work presents the design and implementation of a hardware-based variable DC power supply that combines an ATX SMPS, a 300 W buck converter, monitoring circuits, and a custom 3D-printed enclosure. Emphasis is placed on affordability, modularity, safety, and reproducibility, making the proposed system suitable for academic laboratories and electronics enthusiasts [5], [9].

2.       Literature Review

The design of DC power supplies has evolved from linear regulator–based architectures to high-efficiency switch-mode and hybrid solutions. Early laboratory power supplies relied heavily on linear regulation due to simplicity and low output noise; however, these designs suffer from poor efficiency, excessive heat dissipation, and limited current handling capability, especially under high load conditions [7]. As a result, modern research increasingly favors switch-mode power supplies (SMPS) and DC–DC converter–based solutions.

Udawat et al. [1] provided a comprehensive review of DC variable power supply designs, highlighting the advantages of SMPS-based systems in terms of efficiency, compact size, and cost effectiveness. Their study emphasized that reusing commercially available power modules significantly reduces development cost while maintaining acceptable performance for laboratory applications. Akram et al. [2] demonstrated the design of a regulated DC power supply intended for laboratory use, focusing on voltage stability and load regulation. While their approach achieved good regulation, the design relied on dedicated power stages and did not explore reuse of high-current commercial SMPS units.

The reuse of ATX computer power supplies has gained attention due to their high availability, robust internal protection mechanisms, and multiple regulated output rails. According to the Intel ATX Power Supply Design Guide [6], modern ATX SMPS units incorporate over-voltage, over-current, short-circuit, and thermal protection, making them suitable for experimental environments. Their ability to deliver high current on the 12 V rail makes them particularly attractive for powering DC–DC converters in laboratory power supply designs.

Buck converters are widely used in adjustable power supplies due to their high efficiency and scalability. Texas Instruments’ application report [4] details the design considerations of buck converters, emphasizing PWM control, feedback stability, and current limiting. Erickson and Maksimović [7] further discussed the theoretical foundations of buck converter operation, highlighting the advantages of high-frequency switching for reducing component size and improving transient response. These principles form the basis of the voltage regulation stage used in this work.

Recent studies have also focused on improving usability and safety in laboratory power supplies. Chen and Yang [9] presented an automated power supply unit incorporating digital monitoring to improve operational accuracy and user interaction. Their findings indicate that real-time voltage and current feedback significantly reduces accidental component damage during testing. However, many reported designs lack thermal monitoring or mechanical optimization for compact integration.

Based on the reviewed literature, it is evident that a cost-effective, high-current, and feature-rich variable DC power supply can be realized by combining a recycled ATX SMPS with a high-power buck converter, supplemented by monitoring and protection modules. The present work builds upon these studies by integrating voltage regulation, current limiting, thermal monitoring, and a custom 3D-printed enclosure into a single compact hardware system suitable for educational and laboratory use[10].

3.       Architecture

The overall architecture of the proposed system is shown in Fig. 1. The design is centered around a recycled Foxin 500 W ATX SMPS, which serves as the primary DC source. The ATX supply provides regulated 12 V, 5 V, and 3.3 V rails. The 12 V rail is used as the input to a 300 W DC–DC buck converter to generate the adjustable output voltage.

The system architecture includes:

·         Fixed output rails (12 V, 5 V, 3.3 V)

·         Adjustable DC output (1.2–12.1 V, up to 10 A)

·         Digital volt-amp meter for real-time monitoring

·         Temperature display module for thermal monitoring

·         Current limiting and voltage control potentiometers

·         USB 5 V output module

·         Banana socket output terminals

·         Custom 3D-printed enclosure for mechanical safety and airflow

All components are integrated within a modular enclosure to ensure safe operation, proper ventilation, and ease of use. The architecture of the proposed variable DC power supply is built around a repurposed ATX computer power supply combined with a high-power buck converter and several monitoring modules. The system delivers fixed output rails (12 V, 5 V, and 3.3 V), a high-current adjustable output, and a regulated 5 V USB output. All modules are integrated inside a custom 3D-printed enclosure designed to improve airflow, safety, and component placement.

Fig. 1. Complete Wiring Diagram of the Variable DC Power Supply

Table 1: Cost and specifications of the concept

Hardware Components

A.    Foxin 500 W ATX Power Supply

The Foxin 500 W ATX power supply is used as the primary DC source in the proposed variable power supply as in figure 2. ATX power supplies are widely available at low cost due to their large-scale use in desktop computers, making them an economical option compared to traditional laboratory power supplies. Despite their low cost, ATX units offer high reliability, strong current output, and multiple regulated voltage rails, which makes them suitable for power electronics projects.

Fig. 2. Foxin 500 W ATX Power Supply

Internally, the ATX supply operates as a Switch-Mode Power Supply (SMPS). It converts the 230 V AC mains into low-voltage DC through a sequence of stages including rectification, high-frequency switching, transformer isolation, and feedback regulation. The high-frequency switching allows the use of compact transformers and improves energy efficiency compared to linear power supplies. The ATX unit provides standard regulated rails such as 12 V, 5 V, and 3.3 V, achieved by secondary windings and individual rectification circuits. These rails are designed to remain stable under varying load conditions due to continuous pulse-width modulation control and feedback compensation.

This ATX power supply is chosen for the project because it delivers high current on the 12 V rail, which is required to drive the 300 W buck converter responsible for generating the adjustable output. The 5 V and 3.3 V rails can be used directly as fixed outputs without additional regulation. Its efficiency, safety features, strong current capacity, and low cost make it an ideal foundation for building a multi-output variable DC power supply.

B.    300 W DC-DC Buck Converter Module

Fig. 3. 300 W DC-DC Buck Converter module

The 300 W buck converter module forms the adjustable voltage stage of the power supply in figure 3. A buck converter is a high-efficiency step-down regulator that reduces the 12 V rail from the ATX supply to a lower, controllable output. This module supports output voltages from 1.2 V to 35 V and can deliver up to 10 A, making it suitable for high-current laboratory use.

A 5 kΩ multi-turn potentiometer allows precise adjustment of output voltage, while a 10 kΩ potentiometer provides current limiting, preventing excessive load currents. The converter’s efficiency typically exceeds 90%, reducing heat generation and allowing reliable operation inside the 3D-printed enclosure. Its compact size, strong power capability, and integrated LM358-based feedback control make this module essential for delivering a smooth and adjustable output in the proposed power supply system.

C.    Digital Volt-Amp Meter Module

Fig. 4. Digital Volt-Amp Meter Module

Figure 4 is the Digital Volt-Amp Meter Module the meter consists of two functional parts: a high-impedance voltage sensing circuit and a shunt-based current measurement circuit. The voltage input is connected in parallel with the output terminals, enabling it to measure the exact voltage delivered to the load. Current is measured by passing the load through an internal low-resistance shunt resistor. The voltage drop across this shunt is processed by the module’s internal amplifier circuitry to calculate the current value.

In this project, the digital display is mounted on the front panel and continuously shows both voltage and current of the variable output. This is particularly important because the buck converter supports high currents, and the user must be able to check the load conditions while adjusting the voltage or current limit. The volt-amp meter ensures safe operation, helps in fine-tuning low-voltage outputs, and enhances the overall functionality of the variable power supply.

D.    Temperature Display Module

Fig. 5. Temperature Display Module

The temperature display module is included in the system to provide continuous monitoring of the internal temperature of the power supply. Low-cost temperature displays commonly use an NTC thermistor sensor, in fig. 5, which changes its resistance according to temperature. This resistance variation is processed by the module’s internal amplifier or microcontroller to calculate and display the corresponding temperature value. Such modules are widely used due to their simplicity, fast response, and low cost, making them suitable for compact power electronics applications.

In the proposed design, the temperature sensor is placed near heat-generating components such as the buck converter, heatsinks, or internal wiring. Although the ATX power supply includes its own built-in thermal protection, external temperature monitoring provides an additional layer of safety. It allows the user to observe the thermal condition of the system during high-current operation and ensures that the buck converter and internal components do not exceed safe temperature limits. This is especially important in enclosed spaces, such as the 3D-printed body used in this project, where airflow is limited.

The temperature display on the front panel enables real-time tracking of internal heat buildup, helping the user operate the supply more safely during extended testing sessions. By alerting the user to rising temperatures, the module helps prevent overheating, protects sensitive components, and improves the long-term reliability of the complete power supply system.

E.    Control Potentiometers

Fig. 6. Multi-turn Precision Potentiometer 

   Fig. 7. Standard 10 kΩ Linear Potentiometer

The power supply uses two potentiometers on the front panel to control the adjustable output characteristics provided by the buck converter. These potentiometers allow the user to regulate both the output voltage and the maximum output current, enabling safe and precise operation across a wide range of loads as shown in figure 6 & 7.

F.    USB 5 V Charging Module

The USB 5 V charging module is incorporated into the system to provide a convenient, regulated USB output for powering or charging external devices. This module is a compact DC-DC step-down converter that accepts 12 V from the ATX supply and produces a stable 5 V output, typically capable of delivering up to 2 A. Such modules are commonly used in power banks and automotive chargers due to their small size, efficiency, and compatibility with standard USB-powered electronics.

In this project, the USB module is connected directly to the 12 V ATX rail, providing a separate regulated output independent of the variable voltage output. This separation ensures that the USB-powered devices are always supplied with a clean and stable 5 V, regardless of the adjustments made to the main buck converter. Including this module increases the functionality of the power supply and makes it suitable for a wider range of laboratory and hobbyist applications.

G.    Banana Socket Output Terminals

All fixed and variable outputs are delivered through high-quality banana sockets mounted on the front panel. These terminals provide safe, low-resistance connections for external circuits. The following outputs are available:

●        12 V DC (ATX rail)

●        5 V DC (ATX rail)

●        3.3 V DC (ATX rail)

●        Variable DC: 1.2–12.1 V (from buck converter)

●        USB 5 V output

Banana sockets are color-coded to avoid polarity errors and improve usability.

H.   3D-Printed Enclosure

Fig. 8. CAD Design of the 3D-Printed Enclosure Components

The entire power supply is housed inside a custom 3D-printed enclosure, designed specifically for this project to provide structural support, efficient airflow, and a compact form factor. The enclosure was fully modeled and prepared using Onshape, a cloud-based CAD tool that allowed precise control over dimensions, mounting points, and panel cutouts, as shown in figure 8. The design is intentionally optimized to minimize material usage so that the overall build remains low-cost and easily reproducible for anyone attempting to recreate the power supply [1].

The enclosure consists of three primary 3D-printed components: an upper bracket, a lower bracket, and a front panel. The upper and lower brackets slide onto the ATX power supply and form the mechanical backbone of the enclosure. The front panel holds the user-interface elements including the volt-amp meter, potentiometers, banana sockets, USB output ports, and the temperature display. By printing only these essential parts, the overall material consumption and printing time are significantly reduced.

4. Methodology

The methodology adopted for the design and implementation of the proposed variable DC power supply follows a modular and hardware-centric approach. The development process was divided into distinct stages to ensure reliability, safety, and reproducibility.

4.1 Power Source Selection and Preparation

A Foxin 500 W ATX SMPS was selected as the primary power source due to its low cost, wide availability, and high current capability. Before integration, the ATX power supply was tested independently to verify stable output voltages on the 12 V, 5 V, and 3.3 V rails. The PS_ON signal was permanently grounded to enable continuous operation, as specified in the ATX design guidelines [6]. Dummy load resistors were connected where necessary to ensure stable regulation under low-load conditions.

4.2 Voltage Regulation Using Buck Converter

The adjustable output stage was implemented using a 300 W DC–DC buck converter module powered from the 12 V ATX rail. The converter operates on PWM-based switching, where the duty cycle determines the output voltage. A 5 kΩ multi-turn potentiometer was connected to the feedback network to enable precise voltage adjustment. This configuration allows smooth control of the output voltage from 1.2 V to 12.1 V, in accordance with buck converter design principles discussed in [4], [7].

4.3 Current Limiting and Protection

To enhance safety, current limiting was implemented using the converter’s internal sensing mechanism. A 10 kΩ linear potentiometer was used to adjust the maximum allowable output current. When the load current exceeds the preset limit, the converter reduces the output voltage to prevent damage to both the supply and the connected circuit. This approach ensures protection during short circuits or accidental overloads, which is critical in laboratory environments [2].

4.4 Monitoring and Measurement Integration

Real-time monitoring was achieved using a digital volt-amp meter module connected to the output of the buck converter. The voltage sensing input was connected in parallel with the output terminals, while the current sensing was achieved through an internal shunt resistor. Additionally, a temperature display module with an NTC sensor was placed near high-heat-generating components such as the buck converter and internal wiring. This allows continuous observation of thermal conditions during operation, supplementing the internal protection of the ATX SMPS [6].

4.5 Mechanical Design and Enclosure Fabrication

A custom enclosure was designed using CAD software to house all system components securely. The enclosure was fabricated using 3D printing to reduce cost and allow design flexibility. The mechanical design prioritized airflow, with open side panels guiding air across heat-sensitive components before exiting through the ATX power supply fan. This design approach improves thermal management while maintaining a compact form factor [1].

4.6 System Integration and Testing

All modules were integrated into the enclosure, and electrical connections were secured using heat shrink tubing and insulated wiring. The completed system was tested under various load conditions to evaluate voltage regulation, current handling, and thermal performance. Measurements confirmed stable operation across the full voltage range and reliable current limiting under overload conditions.

5. Results and Discussion

Experimental evaluation demonstrated that the proposed power supply delivers stable fixed outputs and a smooth adjustable output across the specified voltage range. The buck converter maintained voltage regulation under varying load conditions, with efficiency exceeding 90% at moderate loads. The current limiting mechanism effectively protected the system during overload scenarios.

Fig. 9:  Front Panel of the Variable Power Supply (Operational View)

Figure 9 is the front Panel of the Variable Power Supply (Operational View).

The digital volt-amp meter provided accurate real-time measurements, enabling precise voltage and current adjustment. Thermal monitoring confirmed that internal temperatures remained within safe limits during prolonged operation, supported by effective airflow through the enclosure. Compared to commercial laboratory power supplies, the developed unit offers comparable functionality at significantly lower cost.

6. Conclusion

The proposed variable DC power supply successfully delivers multiple fixed outputs along with a stable adjustable output from 1.2 V to 12.1 V at currents up to 10 A. By combining a Foxin 500 W ATX power supply with a 300 W buck converter, the system achieves high efficiency, strong current capability, and reliable regulation suitable for electronics testing and general laboratory use. The addition of a digital volt-amp meter, temperature display, USB output, and current limiting improves safety and usability during operation.

The custom 3D-printed enclosure keeps the unit compact, low-cost, and well ventilated while making the design easy to reproduce. Overall, the project demonstrates a practical and affordable alternative to commercial bench power supplies, offering flexibility, protection features, and stable performance for students, hobbyists, and small labs.

                                ACKNOWLEDGMENT