This project demonstrates a DC-DC buck converter using a 555 timer IC as a PWM generator. The output of the 555 controls an IRLZ44N N-channel MOSFET to step down a 12V DC input to a regulated 5V DC output.
This buck converter is designed to simulate stepping down 230V AC mains power to a safe, low-voltage 5V DC. Due to simulator limitations, the AC front-end has been simplified for practical simulation, but the design intention is fully explained.
In a real-world application, this converter would operate like so:
- AC Input Stage
- 230V RMS @ 50Hz (standard wall outlet for Kurdistan , etc...).
- Step-Down Transformer
- Reduces AC voltage from 230V to ~12V AC.
- Schottky Bridge Rectifier
- Converts AC to pulsating DC.
- Smoothing Filter
- A 10,000µF polarized capacitor smooths out the ripples and delivers ~12V DC.
- Buck Converter Stage
- Steps 12V DC down to 5V DC using PWM switching.
⚠️ Note: The free version of Proteus simulation software does not allow adding too many components. Therefore, the AC-to-DC front-end was omitted in simulation, and a 12V DC source was connected directly to the buck converter stage instead.
- 555 Timer (U1): Configured in astable mode to generate PWM.
- MOSFET (Q1 - IRLZ44N): Acts as a high-speed switch.
- Inductor (L1): Stores and releases energy during switching cycles.
- Diode (D1): A Schottky diode to minimize forward voltage drop and allow freewheeling current.
- Capacitor (C3): Smooths out the pulsed output.
- Load Resistor (R3): Simulates a typical resistive load (500Ω).
555 Timer in Astable Mode:
[ f \approx \frac{1.44}{(R1 + 2R2) \cdot C} ]
Given:
- R1 = 1kΩ
- R2 = 7kΩ
- C = 10nF
[ f \approx \frac{1.44}{(1k + 2 \cdot 7k) \cdot 10nF} = \frac{1.44}{150k \cdot 10^{-9}} \approx 9600 \text{ Hz} ]
- PWM Frequency: ~9.6 kHz
Duty Cycle:
[ D = \frac{R1 + R2}{R1 + 2R2} = \frac{1k + 7k}{1k + 14k} = \frac{8k}{15k} \approx 53.3% ]
Expected Output Voltage:
[ V_{out} = D \cdot V_{in} = 0.533 \cdot 12V \approx 6.4V ]
However, taking into account switching losses and diode drop, the actual simulated output stabilizes closer to 5V DC. with 500 ohm load resistor.
- Input: 12V DC
- Output: ~5V DC (clean and stable)
- Frequency: ~9.6 kHz
- Output Ripple: Low, thanks to the 470µF filter capacitor
- Load: 500Ω resistive
- Software: Proteus 8 (Free Version)
- Simulation Limitations: Limited number of components, so AC rectification stage was not simulated
- Add feedback control using an op-amp to regulate output more precisely.
- Include thermal protection and voltage/current sensing.
- Implement soft start to avoid inrush current.
Feel free to fork the repo and submit pull requests! Suggestions, improvements, and discussions are always welcome.