title: Tutorial 103: PWM Basics¶

Tutorial 103: PWM Basics¶

Overview¶

Pulse-Width Modulation (PWM) is the fundamental control technique in power electronics. This tutorial introduces PWM generation, duty cycle control, and how to apply PWM to switch power semiconductors.

Level: Beginner/Intermediate (⅔)

Duration: 30-35 minutes

Series: Getting Started

Learning Objectives¶

By the end of this tutorial, you will: - [ ] Understand PWM principles and terminology - [ ] Generate PWM signals using control blocks - [ ] Control switch duty cycle - [ ] Observe the relationship between duty cycle and average output - [ ] Build a simple PWM-controlled circuit

Prerequisites¶

• Complete Tutorial 101: First Simulation
• Complete Tutorial 102: Basic Circuits
• Basic understanding of switching converters (helpful)

Materials¶

PWM Fundamentals¶

What is PWM?¶

PWM converts a DC voltage into a pulsed waveform by switching between ON and OFF states at high frequency. The average output is controlled by the duty cycle.

        │ ON │OFF│ ON │OFF│
        ├────┼───┼────┼───┤
    Vin ┤████│   │████│   │  PWM Waveform
        │    │   │    │   │
    0   └────┴───┴────┴───┴────────── Time
        │<──>│   │<──>│
          Ton      Ton
        │<──────>│
           Ts (Period)

Key Parameters¶

Duty Cycle Calculation¶

D = Ton / Ts = Ton × fs

Average Output Voltage¶

For an ideal switch with input Vin:

Vout,avg = D × Vin

Example: Vin = 100V, D = 0.4 → Vout,avg = 40V

PWM Generation Methods¶

Method 1: Comparator-Based PWM¶

Compare a reference (DC or slow-varying) signal with a carrier (triangle or sawtooth):

  Reference (Vref) ──────────────────────────
                     ╱╲    ╱╲    ╱╲    Carrier (Triangle)
                    ╱  ╲  ╱  ╲  ╱  ╲
                   ╱    ╲╱    ╲╱    ╲

  PWM Output:      HIGH when Vref > Carrier
                   LOW when Vref < Carrier

Method 2: Digital Counter¶

1. Counter counts from 0 to N (period)
2. Compare counter with threshold value
3. Output HIGH when counter < threshold

GeckoCIRCUITS Implementation¶

Use CONTROL components: 1. Triangle Generator (SIG): Creates carrier waveform 2. Comparator (CMP): Compares reference with carrier 3. Signal Source: Provides DC reference (duty cycle setpoint)

Building a PWM Generator¶

Step 1: Create Triangle Carrier¶

1. Add Signal Generator (SIG) from CONTROL
2. Configure:
3. Waveform: Triangle
4. Amplitude: 1 (0 to 1 range)
5. Frequency: 10 kHz (switching frequency)
6. Offset: 0.5 (center at 0.5)

Step 2: Add Reference Signal¶

1. Add Constant Source or Signal Generator
2. Set value = 0.5 (for 50% duty cycle)
3. This represents the duty cycle command (0-1 = 0-100%)

Step 3: Create Comparator¶

1. Add Comparator (CMP) from CONTROL
2. Connect:
3. Input A: Reference signal
4. Input B: Triangle carrier
5. Output: HIGH when A > B, LOW when A < B

Step 4: View PWM Output¶

1. Connect comparator output to SCOPE
2. Also connect carrier and reference for comparison
3. Run simulation

PWM Control Circuit¶

Simple Switch with PWM¶

    CONTROL DOMAIN                    POWER DOMAIN
    ┌─────────────────┐              ┌─────────────────┐
    │                 │              │                 │
    │  [Carrier]      │              │  +Vin ──[S]──┬──│
    │      │          │              │         │    │  │
    │     [CMP]───────│──── Gate ────│─────────●    │  │
    │      │          │              │              R  │
    │  [Ref/D]        │              │               │ │
    │                 │              │  GND ─────────┴─│
    └─────────────────┘              └─────────────────┘

Control-Power Interface¶

In GeckoCIRCUITS: - Control signals (SIG, CMP, etc.) connect to gate inputs of power switches - The switch turns ON when gate signal is HIGH (typically > 0.5) - The switch turns OFF when gate signal is LOW

PWM Parameters Effect¶

Varying Duty Cycle (D)¶

Varying Switching Frequency (fs)¶

Higher fs: - Smaller output ripple - Higher switching losses - Smaller filter components

Lower fs: - Larger output ripple - Lower switching losses - Larger filter components

Typical fs: 20 kHz - 200 kHz for power converters

Circuit Example: PWM-Controlled Resistor¶

Build this circuit to see PWM in action:

         Control              Power
    ┌───────────────┐    ┌──────────────────┐
    │               │    │                  │
    │ Vref=0.5  ──┐ │    │  Vin    S.1      │
    │             │ │    │  ┌─┐   ┌───┐     │
    │ Triangle ─┬─┤ │    │  │ │───┤   ├───┐ │
    │ fs=10kHz  │ │ │    │  └─┘   └─┬─┘   │ │
    │           v │ │    │          │   ┌─┴─┐
    │        [CMP]─│─│──gate──      │   │ R │
    │              │ │    │         │   └─┬─┘
    │              │ │    │         └─────┤ │
    └──────────────┘ │    │      GND ─────┘ │
                     │    └─────────────────┘

Expected Results¶

1. Switch Voltage (Vds):
2. 0V when ON

3. Vin when OFF

4. Resistor Voltage (Vr):

5. Vin when switch ON
6. 0V when switch OFF

7. Average = D × Vin

8. Resistor Current:

9. Vin/R when switch ON
10. 0 when switch OFF

Advanced: Modulated PWM¶

Instead of a fixed reference, use a varying reference:

    Sine Wave Reference (Vref)
    ────╱╲────╱╲────╱╲────
       ╱  ╲  ╱  ╲  ╱  ╲

    PWM Output (variable D)
    │██│ │█││██│ │█││██│ │█│

This is the basis for: - Inverters: Create AC from DC - Motor drives: Variable speed control - Audio amplifiers: Class D amplification

Checkpoint¶

At this point, you should: - [ ] Understand duty cycle and its effect on average voltage - [ ] Be able to create a triangle carrier waveform - [ ] Use a comparator to generate PWM - [ ] Connect PWM to a power switch gate - [ ] Observe PWM waveforms in the SCOPE

Common Issues¶

Exercises¶

Exercise 1: Duty Cycle Variation¶

1. Open ex_3_pwm.ipes
2. Vary the reference from 0.2 to 0.8
3. Measure average output voltage at each setting
4. Verify: Vout,avg = D × Vin

Exercise 2: Frequency Effects¶

1. Change fs from 5 kHz to 20 kHz
2. Keep D = 0.5
3. Observe: Output waveform changes

Exercise 3: PWM with LC Filter¶

1. Add an inductor in series with the switch output
2. Add a capacitor to ground
3. Observe: The output becomes nearly DC (ripple removed)

Exercise 4: Sinusoidal PWM¶

1. Replace DC reference with a sine wave (50 Hz, amplitude 0.4, offset 0.5)
2. Observe: PWM width varies sinusoidally
3. This is the basis for inverters!

Summary¶

In this tutorial, you learned: 1. PWM principles: duty cycle, frequency, carrier 2. Comparator-based PWM generation 3. Connecting control signals to power switches 4. The relationship between D and average output 5. Foundation for power converter control

Key Formulas¶

Next Steps¶

Continue your learning with: - Tutorial: 201 - Buck Converter - Apply PWM to real converter - Example: Basic Topologies - Complete converter examples

Tutorial Version: 1.0 Last updated: 2026-02 Compatible with GeckoCIRCUITS v1.0+