In the realm of DIY electronics, power supplies are often the cornerstone of any reliable system. Whether you're powering a microcontroller, an amplifier, or a sensor array, stable and efficient power is non-negotiable. In this project, we focus on designing and building a compact and efficient switch-mode power supply (SMPS) tailored for audio equipment. The core component of this build is the ICE2QR0680Z, an integrated quasi-resonant flyback controller from Infineon Technologies.

This isn’t a general-purpose tutorial or a deep dive into theoretical concepts. Instead, it’s a fully described, tangible DIY project—an actual piece of equipment you can construct and use in your workshop or audio lab. With no need for formulas, code, or data tables, the emphasis here is entirely on concept, construction, and practical integration.

Introduction to the Project

Audio devices like preamps, DACs (digital-to-analog converters), or headphone amplifiers often require clean and stable power. While many hobbyists still rely on linear power supplies, these can be bulky and inefficient. In contrast, SMPS designs—especially those based on advanced controller ICs like the ICE2QR0680Z—are far more compact, thermally efficient, and can provide tightly regulated outputs.

In this project, we build a DIY SMPS that delivers dual outputs: one for analog circuits (±15V) and another 5V rail for digital logic or microcontroller subsystems. The ICE2QR0680Z, with its integrated high-voltage startup cell and burst mode support, offers an elegant and compact solution that’s ideal for this kind of application.

Why the ICE2QR0680Z?

The ICE2QR0680Z is part of Infineon's CoolSET family and is designed specifically for off-line switch-mode power supplies. It includes everything you need to drive a flyback converter: a PWM controller, a startup circuit, overvoltage and overcurrent protection, and it operates in a quasi-resonant mode, which helps improve efficiency and reduce electromagnetic interference (EMI).

The chip is known for:

● Reduced component count

● High efficiency under variable loads

● Integrated protection features

● Suitability for compact designs

These qualities make it ideal for our goal of a reliable power supply for sensitive audio gear.

Defining the Project Goals

The end objective is to create a small, boxed power unit that takes a standard AC input (110–240V) and outputs:

● ±15V for analog circuitry

● 5V for digital control or low-power microcontrollers

The unit must:

● Be compact enough to fit in a standard project enclosure

● Produce minimal noise to avoid audio interference

● Remain thermally stable under load

● Provide protections against short circuits, overvoltage, and thermal overload

Gathering the Materials

Here's what goes into the build:

● ICE2QR0680Z quasi-resonant controller

● Flyback transformer (custom-wound or pre-wound based on output requirements)

● Schottky diodes for output rectification

● Electrolytic and ceramic capacitors for filtering

● High-frequency switching MOSFET (if needed externally, depending on transformer)

● Optocoupler and TL431 or equivalent for feedback regulation

● PCB (custom designed or using a prototyping board)

● Heat sinks (for the controller or diodes)

● Enclosure (preferably with venting or fan mount points)

● Terminal blocks for input and output

● Fuses and thermistors for protection

Optional:

● EMI filter module

● Indicator LED or voltmeter display

● Output ON/OFF switch

Planning the Layout

The design phase starts with drawing out a block diagram of how power flows from the AC mains through the controller, transformer, and finally to the outputs. Components are arranged to minimize the loop areas of high-frequency switching, which is essential for reducing EMI.

Special care is taken in isolating the high-voltage section from the low-voltage outputs, both in physical layout and electrical design. An optocoupler is used to feed back output voltage information to the controller for regulation, maintaining safe isolation between primary and secondary circuits.

Heat-producing components like the switching diode, transformer, and the ICE2QR0680Z itself are arranged near ventilation slots or paired with small aluminum heat sinks.

Assembly and Soldering

After the layout is finalized, either a custom PCB is fabricated, or a carefully wired prototyping board is assembled. The ICE2QR0680Z, being a DIP-8 or DSO-8 package, is relatively easy to work with using a soldering iron. Passive components are placed first, followed by semiconductors and the transformer.

Important assembly considerations:

● Double-check the polarity of capacitors and diodes.

● Keep the high-voltage AC path separate from low-voltage output traces.

● Provide ample creepage distance on the PCB between AC and DC sections.

● Ensure all solder joints are solid and free from cold joints or bridges.

Testing starts with applying AC input through an isolation transformer and checking if the controller begins switching. The presence of an output voltage (even if slightly off) indicates the system is alive.

Verifying Output and Performance

Once powered up, the first step is to measure the output rails using a multimeter. Expect to see ±15V and 5V rails within a 10% tolerance. Fine adjustments to the output can be made by tweaking the resistor divider network on the feedback loop, which communicates with the ICE2QR0680Z via the optocoupler.

Using an oscilloscope, we observe:

● Ripple and noise on the output lines

● Switching waveform across the transformer primary

● Startup behavior and burst mode switching under light load

In our prototype, the quasi-resonant switching results in significantly quieter operation compared to traditional fixed-frequency SMPS designs. This is particularly important for audio equipment, where any ripple can introduce unwanted noise.

Integrating with Audio Equipment

After confirming that the power supply works correctly on its own, it's time to connect it to actual audio gear. This might include:

● A headphone amplifier board

● An op-amp based preamp

● A digital-to-analog converter

● A tube buffer stage (via the ±15V rails)

Connection is done via terminal blocks or soldered leads, ensuring solid contact and strain relief. Upon powering the audio device, listen closely for:

● Hum or buzzing (indicative of power supply noise)

● Heat buildup over time

● Performance stability under different signal loads

With proper EMI filtering and grounding, the ICE2QR0680Z-based supply provides a remarkably clean power source. Music playback remains clean, without background noise, and the system stays cool even during extended sessions.

Safety and Reliability Features

A key aspect of this project is ensuring long-term safe operation. Thanks to the ICE2QR0680Z’s built-in protections, several failure modes are already covered:

● Overcurrent protection automatically shuts down the controller during shorts

● Thermal protection disables switching in case of overheating

● Burst mode reduces power waste under low load

● Under-voltage lockout prevents unstable startups

Additional external protections added include:

● A fuse on the AC input line

● A thermistor for inrush current limiting

● Zener clamping diodes for overvoltage suppression

Together, these features make the power supply not just a functional DIY success, but a safe and dependable one.

Customizing and Enhancing the Design

Once the basic version of the power supply is working well, there's room for customization and improvement. Here are a few ideas to explore:

1. Variable Output: Add a potentiometer in the feedback path to allow adjustable output voltages, useful for powering different devices.

2. OLED Display Module: Mount a small display that shows real-time output voltage and current consumption.

3. Multiple Output Channels: Expand the design to include additional voltage rails such as 12V or 3.3V for more comprehensive support.

4. Battery Backup Integration: Add a battery switchover circuit to keep certain devices powered in case of AC loss.

5. Remote Power Control: Integrate a relay or MOSFET switch triggered via a remote or microcontroller.

6. Universal AC Input: Extend the input range to fully support 90–264V AC, making the supply travel- and export-friendly.

Reflecting on the Build

This project, centered around the ICE2QR0680Z, transforms what might be considered a complex challenge—building a safe and efficient AC-to-DC converter—into a hands-on, manageable endeavor. The result is not only a useful tool for powering audio projects but also a valuable experience in working with switch-mode topologies and high-voltage electronics.

Most importantly, this build helps demystify the design and construction of SMPS systems. The ICE2QR0680Z simplifies many of the tough design decisions, integrating advanced functions into a single compact IC. It also brings industrial-grade reliability to the DIY workspace.

For enthusiasts who frequently build or repair audio systems, having a homemade power supply tailored to those needs is a tremendous asset. It also opens up new avenues for experimentation, whether it's running analog filters, powering microcontrollers, or supporting digital displays.

Conclusion

DIY electronics are about more than just blinking LEDs and sensors. When you take the time to build something fundamental—like a switch-mode power supply—you gain a deep appreciation for the backbone of modern devices. With the ICE2QR0680Z at the heart of this project, you've not only built a power supply; you've created a tool that bridges the gap between raw AC power and sensitive audio electronics.

This project leaves you with more than a working circuit. It instills confidence, builds technical intuition, and sparks ideas for where you can go next—whether that's scaling the design for other voltage needs, embedding it into a larger audio system, or simply enjoying the satisfaction of hearing music powered by something you built with your own hands.