This tutorial has been refined to provide a more professional technical flow, improved code accuracy, and a cleaner presentation. All internal links have been updated to the ee-diary.net domain for consistency.
Building a DIY power inverter using an ATmega328P microcontroller is an excellent way to bridge the gap between embedded systems and power electronics. This project demonstrates how to convert 12V DC from a battery into 220V AC at a frequency of 50Hz, suitable for powering low-wattage appliances.
Components Required
| Component | Description |
|---|---|
| ATmega328P | Microcontroller for precise PWM signal generation. |
| IRFZ44N (x2) | N-Channel Power MOSFETs used as high-speed switches. |
| BC547 (x2) | NPN BJTs used as driver stages for the MOSFET gates. |
| 3P2S Transformer | Center-tapped step-up transformer (approx. 1:19 ratio). |
| 1N4001 (x2) | Flyback diodes for MOSFET transient protection. |
| LM7805 | 5V Voltage regulator for the microcontroller logic. |
| Passive Components | Resistors (1kΩ, 10kΩ); Capacitors (47nF, 4700µF, 0.22µF, 0.1µF). |
Circuit Diagrams
The following diagrams illustrate the power supply regulation, the PWM controller logic, and the MOSFET switching stage.
Technical Circuit Explanation
- PWM Logic: The ATmega328P generates two square wave signals on pins PD3 and PD5. These signals are 180° out of phase, ensuring that only one side of the transformer primary is energized at a time, preventing a short circuit (dead-time management).
- Driver Stage: The microcontroller pins lack the current to drive power MOSFET gates directly at high speeds. BC547 BJTs act as a buffer/driver stage. When a PWM pin goes HIGH, the BJT switches, pulling the MOSFET gate to the required level.
- Push-Pull Switching: The MOSFETs alternate current flow through the two halves of the center-tapped primary winding. This alternating magnetic flux induces a high-voltage AC signal in the secondary winding.
- Filtration: A 47nF capacitor on the secondary helps suppress high-frequency switching noise, resulting in a "modified square wave" that is safer for most AC loads.
- Regulation: The 12V battery source is regulated down to 5V via an LM7805. This ensures the ATmega328P receives a stable voltage regardless of the battery's charge level.
The Firmware (Arduino Code)
// Inverter Controller Code for ATmega328Pconst int pushPin = 3; // PWM Output Aconst int pullPin = 5; // PWM Output Bvoid setup() {pinMode(pushPin, OUTPUT);pinMode(pullPin, OUTPUT);// Ensure both are OFF at startupdigitalWrite(pushPin, LOW);digitalWrite(pullPin, LOW);}void loop() {// Side A CycledigitalWrite(pullPin, LOW);digitalWrite(pushPin, HIGH);delay(10); // 10ms for 50Hz (Total period 20ms)// Side B CycledigitalWrite(pushPin, LOW);digitalWrite(pullPin, HIGH);delay(10);}Note: In the provided code, a 10ms delay creates a 50Hz frequency ($f = \frac{1}{T} = \frac{1}{20ms} = 50Hz$). Using an 8ms delay as seen in some prototypes results in a 62.5Hz frequency.
Practical Applications & Resources
- Emergency Backup: Power LED bulbs or chargers during outages.
- Solar Integration: Convert DC from solar charge controllers into AC. For more on the magnetic components, see What Kind of Transformer is Used in Inverters?
- Educational Prototype: A foundation for learning about H-bridges and SPWM. You can compare this to Arduino-based versions here: Building an Inverter with Arduino.
Safety Guidelines
WARNING: This circuit generates high-voltage AC (220V).Always disconnect the DC source before modifying the circuit.Use a fuse between the 12V source and the transformer center tap.Avoid touching the secondary winding terminals while the circuit is powered.
