How to Design a Buck Converter and drive with Arduino

A buck converter is an efficient DC-DC converter that steps down a higher input voltage to a lower output voltage. In this guide, we will design a simple and efficient buck converter using the IRFZ44N MOSFET, along with a detailed circuit diagram and design steps. We’ll also link to related blog posts to provide additional insights into power supply design and battery management systems.

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What is a Buck Converter?

A buck converter, or step-down converter, is a switching regulator that uses a combination of an inductor, capacitor, diode, and a MOSFET switch to step down the input voltage while maintaining high efficiency. Unlike linear regulators such as the LM7805 or LM317, which dissipate excess energy as heat, buck converters use energy-storing components to transfer power more efficiently.

To understand the differences between these voltage regulation methods, check out LM7805 vs LM317: Which Voltage Regulator Should You Use?.

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Components Required

1. IRFZ44N N-Channel MOSFET: This MOSFET offers low on-resistance ($R_{DS(on)} = 22m\Omega$) and is capable of handling up to 49A, making it suitable for this application.
2. Inductor (L): Select an inductor with an appropriate current rating and inductance value.
3. Capacitors (C$_{in}$ and C$_{out}$): For input/output filtering, choose low ESR capacitors.
4. Schottky Diode (D): A fast-recovery diode such as 1N5819 is ideal for minimal losses.
5. PWM Controller: A microcontroller or dedicated IC can generate the PWM signal to drive the MOSFET.
6. Resistors: For feedback and MOSFET gate drive circuitry.

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Circuit Diagram

Below is the circuit diagram for the buck converter:

You can also combine this buck converter with a lithium-ion auto-cutoff circuit for battery management. Learn more about designing a lithium-ion auto-cutoff battery circuit here.

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Design Steps

1. Determine Input and Output Specifications

• Input Voltage ($V_{in}$): 12V
• Output Voltage ($V_{out}$): 5V
• Output Current ($I_{out}$): 2A

2. Choose Switching Frequency

• Typical buck converters operate in the range of 20kHz to 100kHz. For this design, we use 50kHz.

3. Calculate Inductor Value

Use the formula:

$$L = \frac{V_{out} \cdot (1 - D)}{f \cdot \Delta I}$$

Where:

• $D = \frac{V_{out}}{V_{in}}$ is the duty cycle
• $f$ is the switching frequency
• $\Delta I$ is the ripple current

4. Select Capacitors

• Use a low ESR capacitor for $C_{out}$ to minimize output voltage ripple.

5. Choose the Schottky Diode

• The diode must withstand the peak current and reverse voltage.

6. Driver Circuit for IRFZ44N

• The IRFZ44N requires a sufficient gate drive voltage ($V_{GS}$). Ensure your PWM signal is high enough to turn the MOSFET fully on.

Arduino as PWM driver for Buck Converter

To control a 5V bulb load using PWM with an Arduino Uno, you can use one of its PWM-capable pins (3, 5, 6, 9, 10, or 11). The analogWrite() function generates a PWM signal with a default frequency of approximately 490Hz.

Circuit Diagram

Shown below is a circuit diagram in which Arduino generates a PWM signal based on the position of a 10kΩ potentiometer connected to analog pin A0. The potentiometer value will control the duty cycle of the PWM signal.

Code to Generate PWM Signal:

Here’s the Arduino code that generates a PWM signal based on the position of a 10kΩ potentiometer connected to analog pin A0. The potentiometer value will control the duty cycle of the PWM signal.

// Pin definitions
const int potPin = A0; // Potentiometer connected to A0
const int pwmPin = 6;  // PWM output pin

void setup() {
  pinMode(pwmPin, OUTPUT); // Set PWM pin as output
}

void loop() {
  // Read the potentiometer value (0 to 1023)
  int potValue = analogRead(potPin);

  // Map the potentiometer value (0-1023) to PWM range (0-255)
  int pwmValue = map(potValue, 0, 1023, 0, 255);

  // Output the PWM signal to the bulb
  analogWrite(pwmPin, pwmValue);
  
  // Small delay to stabilize reading
  delay(10);
}