Push-Pull Inverter 12V to 220V

Project Overview: Building a 12V to 220V Push-Pull Inverter

In this project, we design and construct a 12V to 220V push-pull inverter. This circuit is specifically designed to convert 12V DC into 220V DC, making it suitable for powering devices with AC input that internally use a bridge rectifier, such as power supplies, phone chargers, laptop chargers, TVs, and computers. However, it is not suitable for inductive devices like fans or transformer-based power supplies without additional modifications.

To power all AC appliances, this circuit must be used in conjunction with a full-bridge inverter stage that converts 220V DC to 220V AC. Below, we outline the steps to build the inverter, including calculations, components, and considerations.

Key Components and Requirements

Ferrite Core Transformer:
- Acts as the main step-up component for converting 12V to 220V DC.
- You can purchase one or recycle from old devices such as ATX power supplies.

To recycle ferrite trasformer watch:

To buy watch:

Circuit:

Driver IC:
- SG3525: Used for generating the high-frequency PWM signal to drive the MOSFETs.
MOSFETs:
- Power transistors for the push-pull configuration, switching the 12V input through the transformer.
Capacitors:
- Input and output capacitors to filter and smooth the voltage.
Fast Recovery Diodes:
- FR207: Used for rectification after the transformer.

Transformer Design and Calculations

Transformer Type:

Ferrite core transformer (e.g., EE15).

Specifications:

Input Voltage (Vin): 12V DC
Output Voltage (Vout): 220V DC
Frequency (f): 50 kHz

Steps to Calculate Windings:

Core Cross-Section Area (Ae):
- Measure or obtain the cross-sectional area of the core from the datasheet.
- For EE15, assume Ae=1.5 cm2=0.00015 m2A_e = 1.5 \, \text{cm}^2 = 0.00015 \, \text{m}^2Ae=1.5cm2=0.00015m2.
Turns Per Volt (TPV):
TPV=1044.44×f×Bmax×Ae\text{TPV} = \frac{10^4}{4.44 \times f \times B_{\text{max}} \times A_e}TPV=4.44×f×Bmax×Ae104
Where:
- BmaxB_{\text{max}}Bmax: Maximum magnetic flux density (e.g., 0.2T for ferrite core).
- fff: Operating frequency (50 kHz).
Substituting values:
TPV=1044.44×50×103×0.2×0.00015\text{TPV} = \frac{10^4}{4.44 \times 50 \times 10^3 \times 0.2 \times 0.00015}TPV=4.44×50×103×0.2×0.00015104 TPV≈15 turns/volt\text{TPV} \approx 15 \, \text{turns/volt}TPV≈15turns/volt
Primary Winding:
- Input voltage: 12V.
- Turns: Np=12×15=180 turnsN_p = 12 \times 15 = 180 \, \text{turns}Np=12×15=180turns.
Secondary Winding:
- Output voltage: 220V.
- Turns: Ns=220×15=3300 turnsN_s = 220 \times 15 = 3300 \, \text{turns}Ns=220×15=3300turns.
Wire Selection:
- Choose wire gauge based on the current requirements. Use thicker wire for the primary winding since it carries higher current.

Circuit Design

Push-Pull Inverter Circuit:

Transformer Connections:
- The primary winding is split into two equal halves, each driven by a MOSFET in the push-pull configuration.
- The center tap is connected to the 12V DC supply.
Driver Circuit:
- Use the SG3525 IC to generate a 50 kHz PWM signal.
- Configure SG3525 with appropriate timing components (resistors and capacitors) to set the frequency.
- The outputs from SG3525 are fed to the MOSFET gates via gate resistors.
MOSFET Selection:
- Choose MOSFETs with a low RDS(on)_{\text{DS(on)}}DS(on) and sufficient voltage and current ratings.
Output Rectification:
- After the transformer, use FR207 fast recovery diodes to rectify the high-frequency AC voltage.
- Add output capacitors to smooth the rectified voltage.

Final Assembly and Testing

Circuit Assembly:
- Assemble all components on a breadboard or PCB.
- Ensure proper soldering of components and connections to prevent short circuits.
Testing:
- Use a variable power supply to provide 12V DC to the circuit.
- Measure the output voltage using a multimeter. It should be close to 220V DC.
Load Testing:
- Connect the output to a suitable resistive load (e.g., a light bulb) to verify performance.

Additional Considerations

Heat Dissipation:
- Use heat sinks on the MOSFETs to manage heat generated during operation.
Safety:
- Ensure proper insulation and safe handling, as high voltages are present in the circuit.
Next Steps:
- To power inductive loads or AC appliances, integrate this circuit with a full-bridge inverter stage to convert 220V DC to 220V AC.

Conclusion

This project demonstrates how to construct a simple and efficient 12V to 220V push-pull inverter. By carefully designing the ferrite core transformer and using appropriate circuit components, this inverter can serve as a foundation for more advanced systems capable of powering a variety of electronic devices.

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