ClassDamp

🔊 Discrete Class-D Amplifier – KiCad + ngspice Simulation

This repository contains the complete design of a fully discrete Class-D audio amplifier built using simple, commonly available analog components such as a 555 timer, LM393 comparator, MOSFET half-bridge, and an LC output filter. The entire design is created in KiCad, and simulated using ngspice. No dedicated Class-D ICs are used — this project demonstrates the fundamental principles behind PWM-based audio amplification.

Repository Structure

C:.
│   classDamp.kicad_pcb        → PCB layout (2-layer board)
│   classDamp.kicad_prl        → KiCad project local data
│   classDamp.kicad_pro        → KiCad project file
│   classDamp.kicad_sch        → Main KiCad schematic
│   fp-info-cache              → KiCad footprint cache
│   readme.md                  → Documentation (you are reading this)
│
├───classDamp-backups          → Automatic KiCad backups
│       *.zip                  → Time-stamped backup archives
│
├───footprints                 → Custom footprint library
│       LM393.kicad_sym
│       478CKS010M.kicad_sym
│       MFR-25FBF52-1K.kicad_sym
│
└───models                     → SPICE models for simulation
        555_timer.lib          → NE555/TLC555 model
        LM393.lib              → LM393 comparator model

🧩 Project Overview

This design implements a single-channel Class-D amplifier using:

555 Timer (triangle generator)

Produces ~100 kHz triangular carrier waveform for PWM.

LM393 Comparator

Compares audio input with triangle wave → produces PWM.

N-MOSFET Half-Bridge

Switches the supply voltage at high frequency based on PWM.

LC Output Filter

Reconstructs the audio from PWM.

KiCad Simulation (ngspice)

All active components (555, comparator, MOSFETs) use custom SPICE models stored in /models/.

📐 Design Steps

1. Triangle Wave Generator (555 Timer)

• Configured in astable mode
• RA, RB, and C chosen for ~100 kHz carrier
• The node at pins 2/6 generates the triangular waveform used for PWM

2. PWM Generation (LM393 Comparator)

• Audio input is compared against the triangle
• Comparator output → PWM with duty cycle proportional to audio amplitude
• Pull-up resistor on output ensures clean logic waveform

3. Power Switching Stage

• Logic-level MOSFETs used in half-bridge configuration
• Gate resistors + pulldown resistors included
• Driver stage isolates comparator from MOSFET gates

4. Output Low-Pass Filter

• LC filter chosen to remove switching frequency (100 kHz)
• Designed with Fc ≈ 20 kHz using: [ F_c = \frac{1}{2\pi \sqrt{LC}} ]

5. Simulation Workflow

• ngspice model files included:

  • models/555_timer.lib
  • models/LM393.lib

• Simulation setup in KiCad:

  .include "./models/555_timer.lib"
  .include "./models/LM393.lib"
  .tran 50n 5m

• Simulations validate:

  • Triangle waveform
  • PWM modulation
  • Switching node waveform
  • LC output reconstruction

🛠️ PCB Details

PCB File: classDamp.kicad_pcb

Key design rules followed:

• 2-layer design
• Bottom layer: solid ground plane
• Top layer: power + signal routing
• Short gate traces for MOSFETs
• Wide copper for high-current paths
• Decoupling capacitors close to supply pins
• LC filter placed near MOSFET switching node

Footprints are stored in /footprints/ and referenced inside the KiCad project.

📦 Models

Stored in models/:

555_timer.lib

SPICE model for NE555 / TLC555 Used for generating triangle wave.

LM393.lib

Dual-comparator SPICE model Used for PWM modulation.

These models have been formatted to be ngspice-compatible and used directly inside KiCad simulations.

📊 Simulated Outputs

The simulation verifies the following:

Triangle Wave (~100 kHz)

From 555 timer pin 2/6.

PWM Output

Duty cycle changes based on audio input (sine wave).

Switching Node Waveform

High-frequency MOSFET switching.

Filtered Audio Output

LC filter reconstructs original analog audio.

🎧 How to Run Simulation

1. Open the project in KiCad

2. Open the schematic (classDamp.kicad_sch)

3. Ensure the .lib files paths are correct

4. Open Simulation → Run Simulation

5. Use .tran 50n 5m or suitable transient analysis

6. Plot:

   • V(triangle)
   • V(pwm)
   • V(switch_node)
   • V(output)

🔧 Features of This Project

• Fully open-source toolchain
• No dedicated Class-D amplifier ICs
• From scratch design → PWM to H-bridge to LC
• Custom SPICE models
• Complete KiCad schematic + PCB
• Modular and easy to expand (dual-channel, feedback, etc.)

🚀 Future Improvements

• Add closed-loop feedback for distortion reduction
• Add proper MOSFET driver (IR2110, IRS2092, etc.)
• Improve LC filter for lower ripple
• Add overload and thermal protection
• Increase power by using 24–36 V supply

📄 License

This project can be released under MIT, GPL, or any open license you prefer. (You can let me know and I’ll insert an appropriate license section.)

🙌 Author Notes

This repository contains backups showing continuous progress, model files, and custom footprints for analog simulation and PCB layout exploration.