Switch Mode Power Supplies (SMPS) are essential in modern electronics, providing efficient power conversion with minimal energy loss. In this DIY project, we will design and construct a compact SMPS capable of outputting either 5V or 12V using the VIPER17LN, a versatile and efficient offline switcher IC. The project is ideal for powering microcontrollers, small appliances, or even as a bench power supply for other DIY projects.

Why VIPER17LN?

The VIPER17LN combines a PWM controller with a power MOSFET, making it a compact solution for creating flyback-based SMPS designs. Its ability to operate directly from the mains (85–265V AC) without requiring complex circuitry makes it an excellent choice for DIY applications. Additionally, its integrated protections, such as overvoltage, overcurrent, and thermal shutdown, ensure reliability and safety.

Project Overview

The goal of this project is to create a reliable SMPS that takes a standard AC input (110V/230V) and provides a regulated DC output of 5V or 12V at up to 1A. The project involves designing a flyback converter circuit around the VIPER17LN, assembling the components, and testing the final output.

Required Components

Here is a list of components you’ll need for this project:

● VIPER17LN: The main switching IC.

● Transformer: A flyback transformer suitable for 5V/12V outputs.

● Input Filter Components:

—  X-class capacitor: 0.1µF or similar.

—  Common-mode choke.

● Rectifier Diodes:

—  Fast recovery diodes for the secondary side.

● Capacitors:

—  Electrolytic capacitors for input and output filtering.

—  Ceramic capacitors for decoupling.

● Resistors:

— For setting feedback and current sensing.

● Optocoupler:

— For feedback isolation.

● Zener Diode:

— For voltage regulation in the feedback loop.

● PCB: Custom PCB or prototyping board.

● Heat Sink: For the VIPER17LN if necessary.

● Enclosure: A plastic or metal case to house the circuit.

Project Steps

1. Understanding the Circuit

At its core, this project revolves around the VIPER17LN operating in a flyback configuration. The flyback transformer isolates the input and output sides, while the IC handles high-frequency switching to convert the AC input into a stable DC output. Feedback through an optocoupler ensures the output remains regulated, even as the load varies.

2. Preparing the Power Stage

The power stage includes the transformer, the VIPER17LN, and associated filtering components.

AC Input

The circuit begins with an AC input stage. Use an X-class capacitor and a common-mode choke to suppress noise and EMI from the mains supply. These components are crucial for passing regulatory standards and preventing interference with other devices.

Transformer

The transformer is the heart of the flyback converter. Choose or wind a transformer with appropriate primary and secondary windings for the desired output voltage and current. For this project, the secondary winding should be configured for 5V or 12V output.

Switching and Filtering

The VIPER17LN controls the transformer’s primary winding. On the secondary side, a fast recovery diode rectifies the output, and electrolytic capacitors smooth the voltage.

3. Feedback and Regulation

To maintain a stable output voltage, a feedback loop is implemented. The output voltage is monitored by a resistive divider and a Zener diode, which provide a reference voltage. An optocoupler transmits this information to the VIPER17LN while maintaining isolation between the primary and secondary circuits.

4. Safety Features

The VIPER17LN includes built-in protections, but additional safeguards can be added for reliability:

● Fuses: Place a fuse at the input to protect against overcurrent.

● Thermistor: Use an NTC thermistor to limit inrush current.

● Snubber Circuit: Add a snubber across the transformer’s primary winding to absorb voltage spikes caused by switching transients.

5. Assembly

Step 1: Layout Planning

Design a PCB or use a prototyping board to lay out the components. Keep the high-voltage and low-voltage sections separate to minimize interference and ensure safety.

Step 2: Soldering Components

Start with smaller components like resistors and capacitors, then move on to larger components like the transformer and VIPER17LN. Ensure proper orientation for polarized components such as electrolytic capacitors and diodes.

Step 3: Heat Management

Attach a heat sink to the VIPER17LN if it heats up significantly during operation. Good ventilation in the enclosure also helps dissipate heat.

6. Testing the Circuit

Before powering the circuit, double-check all connections and verify the component placement.

● Initial Power-Up:

— Use a Variac (variable transformer) to gradually apply AC voltage while monitoring the output.

— Measure the output voltage with a multimeter. It should be close to the desired 5V or 12V.

● Load Testing:

— Connect a resistive load or an electronic load to test the circuit under different conditions.

— Verify that the output remains stable and within specification.

● Ripple and Noise:

— Use an oscilloscope to check for ripple and noise on the output. Excessive ripple may require additional filtering.

7. Enclosing the Circuit

Once the circuit is tested and working reliably, place it in a suitable enclosure. Ensure that:

● All high-voltage parts are properly insulated.

● The enclosure has adequate ventilation to dissipate heat.

● Input and output connections are secure and labeled.

Applications

This SMPS design has several practical applications:

1. Microcontroller Power Supply: Provides clean power for Arduino, ESP32, or Raspberry Pi projects.

2. Battery Charger: Charges batteries with a regulated voltage output.

3. Bench Power Supply: A compact and efficient solution for DIY electronics testing.

4. Home Automation: Powers sensors and relays in IoT projects.

Challenges and Solutions

1. Noise Issues:

● High-frequency switching can cause electromagnetic interference. Proper PCB layout and filtering components can mitigate this.

2. Heat Dissipation:

● Ensure sufficient cooling for the VIPER17LN. If the IC overheats, it may enter thermal shutdown.

3. Transformer Selection:

● An improperly designed transformer can lead to inefficiency or instability. Follow the datasheet recommendations or purchase a pre-designed flyback transformer.

4. Component Sourcing:

● Ensure all components, especially the transformer and optocoupler, meet the required specifications.

Why Build This Project?

Building an SMPS using the VIPER17LN is a fantastic way to learn about power electronics and create a practical tool for your DIY projects. This project demonstrates how modern ICs simplify the design process, allowing hobbyists to create efficient and compact circuits that were once the domain of professionals.

With its versatility and reliability, the completed SMPS is a valuable addition to any electronics workspace. Whether powering your projects or serving as a learning tool, this design is an excellent example of combining theory with hands-on building.

Conclusion

This DIY project showcases how the VIPER17LN can be used to create a compact, efficient, and reliable SMPS for various applications. By following the steps outlined above, you can build a power supply that not only meets your needs but also provides a deeper understanding of switch-mode power design.