⚡ 15W Digital Flyback Converter
Fully Automated CCCV Power Supply with STM32 Control

A sophisticated power electronics project combining digital control, embedded firmware, and precision PCB design

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📋 Project Overview

This project demonstrates the complete design and implementation of a 15W Constant Current / Constant Voltage (CCCV) Flyback Converter with full digital control via STM32L011 microcontroller. The system demonstrates expertise in power electronics, embedded systems, firmware development, and industrial automation.

🎯 Core Challenge

Development of a production-grade power supply capable of:

• Wide Input Range: 230V AC compatibility (multi-national)
• Dual Output Modes: Automatic CC→CV switching for LED applications
• Digital Control: MCU-based regulation with ±2% accuracy
• User Interface: Computer software for real-time output configuration and monitoring
• Industrial Features: Relay feedback contact, 4-stage dimming, external control, comprehensive protection
• Reliability: Production-ready firmware with error handling and EMC compliance

✅ Solution Delivered

A complete power supply system consisting of:

• STM32L011 MCU: ARM Cortex-M0+ with integrated ADC and PWM capabilities
• Flyback Topology: Galvanically isolated 230V AC to variable DC output
• Digital Regulation: PWM-based feedback via digital isolator
• Communication: Serial UART interface for computer control
• Precise Measurement: ADC measurements for voltage and current
• KiCad PCB Design: 6 iterative versions from prototype to production (V1-V6)
• Comprehensive Testing: EMC compliance (CISPR 32 Class A), efficiency measurements, thermal characterization

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🛠️ Technical Architecture

Hardware Stack

• MCU: STM32L011 (ARM Cortex-M0+, 32KB Flash, 8KB RAM)
• Power Topology: Galvanically isolated Flyback Converter
• Input Stage: 230V AC rectification with EMI filter
• Output Control: PWM switching (MOSFET) with frequencies from 22-120kHz
• Measurement: 12-bit ADC (base resolution)
• Communication: UART interface
• Feedback Elements: Digital isolator, relay output for status indication

Software Stack

Layer	Technology	Purpose
Application	C (STM32CubeIDE)	Digital control algorithm (PI/Cascade), state machine, command processing
Driver	LL-Driver (Low-Level)	Direct register access for GPIO, ADC, PWM, UART, DMA
Control Algorithm	PI / Cascaded Control Loop	Maintains stable CC/CV setpoints
Memory	EEPROM	Persistent configuration storage
Monitoring	MCU Tracer	Real-time debugging and performance metrics logging
Communication Protocol	Serial UART	Command interface for PC software integration

System Architecture Diagram

┌─────────────────────────────────────────────────────────────┐
│            PC Control Software (Serial Interface)           │
│  ┌────────────────────────────────────────────────────────┐ │
│  │  Configuration │ Real-Time Monitoring │ Logging        │ │
│  │  • Output V/I  │ • Voltage/Current    │ • Data Export  │ │
│  │  • Dimming     │ • Temperature        │ • Waveforms    │ │
│  │  • Limits      │ • Power Efficiency   │ • Events       │ │
│  └────────────────────────────────────────────────────────┘ │
└────────────────────┬────────────────────────────────────────┘
                     │ UART
        ┌────────────┴────────────┐
        │                         │
    ┌───▼──────────┐      ┌──────▼────────┐
    │  STM32L011   │      │  Power Stage  │
    │  MCU         │      │  & Sensing    │
    │              │      │               │
    │ • ADC Sampl. │      │ • PWM Driver  │
    │ • PI Control │      │ • MOSFET Gate │
    │ • PWM Gen.   │      │ • Voltage FB  │
    │ • UART Comm. │      │ • Current FB  │
    │ • Protection │      │ • Temp Sense  │
    └───┬──────────┴──────┬───────────────┘
        │                 │
    ┌───▼─────────────┬───▼─────────┐
    │                 │             │
┌───▼─┐  ┌────────┐ ┌─▼───┐  ┌──────▼──┐
│Relay│  │Dimming │ │Gate │  │Feedback │
│Out  │  │Input   │ │Drv  │  │Digital  │
└─────┘  └────────┘ └─────┘  └ Isolator┘

230V AC Input → Rectification → Flyback Transformer
→ Secondary Output → Measurement → MCU Feedback → PWM Adjustment

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🎓 Key Technical Achievements

🚀 From Prototype to Production

V1-P: First Prototype

V5: Final Production

The evolution from initial concept to market-ready product, demonstrating continuous refinement through 6 design iterations.

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1️⃣ Digital Power Conversion with Precision Feedback

Challenge: Maintain voltage/current stability across the entire load range.

• Solution: Cascaded/PI control loop with 16kHz (62.5µs) cycle time.
• Innovation: Software-based regulation enables dynamic adjustments and protection functions.

2️⃣ Multi-Mode Power Supply with Automatic Switching

Challenge: Seamless CC/CV operation for diverse loads (LEDs, laboratory applications).

Constant Current Mode (CC):

• Fixed current output (programmable 0A - 1.2A)
• Automatic voltage limiting
• Ideal for LED strings

Constant Voltage Mode (CV):

• Fixed voltage output (programmable 10V - 60V)
• Current limiting for protection
• Standard laboratory power supply functionality

Technical Implementation:

• Software regulation automatically selects the most restrictive controller (voltage or current).
• Seamless transition without overshoot.

3️⃣ Comprehensive Hardware Integration & Protection

Challenge: Integration of analog control, digital MCU, high-voltage power stage, and protection circuits.

Solution: Integrated multi-layer PCB design with:

• Isolated Feedback: PWM transmission via digital isolator for safe control.
• Measurement Acquisition: Voltage and current measurement via shunt and differential amplifier.
• Relay Feedback: Status output for relay contact.
• Dimming Input: 4-stage external dimming.

4️⃣ Robust Firmware Architecture for Production Readiness

Challenge: Creation of reliable, maintainable firmware for embedded power control.

Solution: Structured C codebase with:

• State Machine: Manages boot, regulation, fault detection, and shutdown.
• Safety Features: Overvoltage (OVP) and overcurrent protection (OCP), brownout detection, and watchdog.
• Monitoring System: "MCU Tracer" logs performance metrics for debugging and validation.

5️⃣ PCB Evolution & Design Iteration

Six Production Iterations:

Version	Focus	Status
V1-P	IC voltage supply prototype	✅ Learning phase
V1	First Flyback LED converter	✅ Validated
V2-P	Enhanced design iteration	✅ Refined
V3-P	Further optimization	✅ Tested
V4-Release	Production candidate	✅ Manufacturing ready
V5	Final Production	✅ Active
V6	Next-generation planning	✅ In Production

Design Improvements:

• Thermal management optimization (V1→V5)
• PCB layout for EMC compliance
• Component placement for manufacturing efficiency
• High-voltage isolation routing

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📊 Project Specifications

Category	Details
Input Voltage	230V AC, RMS
Output Power	15W
Output Modes	Constant Current (0A - 1.2A) / Constant Voltage (10V - 60V)
Accuracy	±2% (design target)
Isolation	Galvanic isolation via Flyback transformer
Communication	Serial UART
MCU	STM32L011
ADC Resolution	12-bit base, 14-bit with oversampling
PWM Frequency	22kHz - 120kHz (depending on load)
Protection Features	OVP, OCP, OTP, UVP, short-circuit protection, no-load protection
Relay Output	Status contact
Dimming Control	4-stage via external contacts
Efficiency	> 80% (typical)
Development Time	Bachelor thesis
Team Size	Dr. Michael Heidinger and Ans1S

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🔧 Technical Implementation Highlights

Real-Time Digital Control

• Control cycle at 16kHz (62.5µs cycle time)
• DMA-based data transfer from ADC
• PWM resolution optimized via Farey sequence
• Multi-mode operation with automatic CC/CV transition

Precision Measurement & Feedback

• Current measurement via shunt resistor and differential amplifier
• Voltage measurement via voltage divider and differential amplifier
• ADC calibration and offset correction in firmware
• Thermal management

Embedded Communication Protocol

• ASCII-based UART commands
• Real-time telemetry streaming (voltage, current)
• Error reporting

Power Electronics Design

• Storage transformer dimensioning
• MOSFET selection and snubber design
• EMC compliance (CISPR 32) via EMI filtering
• Longevity through elimination of electrolytic capacitors

Why This Matters: The system demonstrates understanding of complete power supply design—from AC mains to regulated DC output—combining digital control with analog power electronics.

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📈 Simulation & Analysis

Comprehensive Design Validation

SPICE Simulation (LTspice):

• Flyback converter operation modeling
• Transient response analysis (load steps)
• Efficiency calculations

Power Flow Analysis (Plecs):

• System-level power distribution modeling
• Harmonic analysis for EMC prediction
• Thermal loss estimation

Results:

• ✅ Output current ripple below 133mApp
• ✅ Transient settling within design specification
• ✅ EMC compliance validated

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📊 Measurement Results & Characterization

Performance Validation

┌─────────────────────────────────────────────────────────┐
│     15W Flyback Converter Performance Data              │
├─────────────────────────────────────────────────────────┤
│ Constant Current Accuracy   │ ±1.8% @ 1.2A setpoint     │
│ Constant Voltage Accuracy   │ ±2.1% @ 48V setpoint      │
│ Load Transient Response     │ 45ms (design target)      │
│ Output Voltage Ripple       │ 85mV peak @ 1.2A CC       │
│ Output Current Ripple       │ < 133mA peak-to-peak @ 24V│
│ Full-Load Efficiency        │ 82.5% @ 15W (target)      │
│ Thermal Steady-State (25°C) │ +22.9°C (MOSFET @ 47.7°C) │
│ Protection Response Time    │ < 2ms (software)          │
│ UART Command Latency        │ < 10ms (design target)    │
└─────────────────────────────────────────────────────────┘

EMC Testing (Electromagnetic Compatibility)

• ✅ CISPR 32 Class A (conducted emissions)
• ✅ EN 55015 Radiated Emissions (below limits)
• ✅ EN 61000-4-2 ESD Immunity (±8kV contact)
• ✅ EN 61000-4-4 Burst Immunity (2kV)
• ✅ EN 61000-6-2 Industrial Immunity

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🛠️ Created With

• KiCad - PCB design and schematic capture (all 6 iterations)
• STM32CubeIDE - Embedded firmware development
• LTspice - Power electronics simulation
• Plecs - Energy system modeling
• STM32CubeMX - MCU peripheral configuration
• J-Link - SWD debugger for firmware upload & debugging

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🚀 Key Learning Outcomes

This project demonstrates comprehensive competencies in:

Competency	Implementation
Power Electronics Design	Flyback topology, transformer dimensioning, MOSFET selection, thermal analysis
Digital Control Systems	PI/cascaded control loops, ADC sampling, PWM modulation
Embedded Firmware	STM32 LL drivers, interrupt handling, UART communication, DMA
PCB Design & Manufacturing	KiCad schematic & layout, layer stackup, EMC-compliant routing, 6+ design iterations
Testing & Validation	EMC compliance (CISPR 32), efficiency measurement, thermal characterization
System Integration	Combination of analog power, digital control, and communication
Problem Solving	Iterative refinement, simulation-driven design, experimental validation

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🎯 Why This Project Stands Out

1. Complete System Design: Not just firmware or just hardware—full integration from AC mains to regulated DC output.
2. Production-Grade Quality: 6+ design iterations demonstrate mature engineering approach.
3. Real-World Complexity: Mastery of galvanically isolated power conversion with digital feedback.
4. Comprehensive Validation: Simulation, measurement, and EMC testing all documented.
5. Scalability: Architecture supports future enhancements.
6. Documentation: Mathematical models, technical datasheets, and detailed measurements included.

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💡 Technical Insights & Design Decisions

Challenge 1: Stability in Flyback Converter Operation

• Problem: Flyback converters tend to exhibit ripple and load-dependent variations.
• Solution: Tight digital PI control loop and careful hardware design (snubber).
• Learning: Digital control can effectively compensate for analog non-idealities.

Challenge 2: PCB Layout for High-Voltage Isolation & EMC

• Problem: AC mains and isolated secondary side require careful routing.
• Solution: Proper creepage/clearance, separate ground planes, EMI filtering.
• Learning: EMC compliance must be designed in from the start.

Challenge 3: Firmware Reliability in a Power Supply

• Problem: Watchdog timeouts or firmware crashes could damage the load.
• Solution: Redundant protection mechanisms (hardware OCP/OVP + software OVP/UVP), safe-state defaults.
• Learning: Mission-critical embedded systems require defensive programming.

Challenge 4: Thermal Management at 15W in Compact Package

• Problem: Limited PCB area with high power dissipation.
• Solution: Thermal measurements, optimal placement of power components (MOSFET, diode).
• Learning: Thermal design is integral to electrical design (hottest spot 47.7°C).

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📞 Project Collaboration

This project was developed in collaboration with:

• Dr. Michael Heidinger - Digital Power Systems (Project supervision and technical guidance)
• Prof. Dr. rer. nat. Uli Lemmer - Lichttechnisches Institut (LTI), Karlsruhe Institute of Technology (KIT) (Academic supervision and institutional support)

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📄 Additional Resources

• Product Datasheet: Datasheet/DIG-CCCV-15W_datasheet.pdf - Official technical specifications and operating guidelines

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Engineered with precision. Tested for reliability. Built to production standards.

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