Understanding and Calculating PWM Time Period

Pulse Width Modulation (PWM) is a fundamental concept used in a variety of applications, such as controlling the brightness of LEDs, driving servos, and voltage regulation. The PWM time period is a crucial parameter that determines the duration of one complete cycle of the PWM signal, which includes both the high on and low off states. This article will guide you through the steps and formula to calculate the PWM time period, as well as cover related concepts and applications.

Introduction to PWM

PWM stands for Pulse Width Modulation, which is a digital signal used to control the duration of the on and off periods of a square wave. This technique is widely used in electronic circuits and systems to regulate output voltage, brightness, and speed.

Formula and Steps to Calculate PWM Time Period

The PWM time period is calculated using the formula:

T 1 / f

Where:

T is the PWM time period in seconds. f is the frequency of the PWM signal in hertz (Hz).

Steps to Calculate PWM Time Period:

Determine the Frequency: Start by identifying the frequency of the PWM signal. This is typically specified in hertz (Hz) and set in the microcontroller or PWM generator configuration. Apply the Formula: Use the formula T 1 / f to calculate the time period.

Example:

If the PWM frequency is 1 kHz (1000 Hz), the time period can be calculated as follows:

T 1 / 1000 0.001 seconds 1 ms

Additional Considerations

Duty Cycle

The duty cycle is the percentage of time the signal is high compared to the total time period. It is often expressed as a percentage:

Duty Cycle (High Time) / T * 100

High and Low Times

If you know the duty cycle and the time period, you can calculate the high and low times:

High Time T * (Duty Cycle / 100) Low Time T - High Time

Applications of PWM

PWM in Electronic Circuits

A common way we use PWM here at [SparkFun] is to control the dimming of RGB LEDs or the direction of a servo motor. PWM is a square wave with a varying high and low time. A basic PWM signal is shown in the figure below:

Figure 1: Pulse width modulation wave

On-Time and Off-Time

As shown in the figure, Ton denotes the on-time and Toff denotes the off-time of the signal. Period is the sum of both on and off times:

Period Ton Toff

Duty Cycle

Duty cycle is calculated as the ratio of on-time to the period of time:

Duty Cycle On-Time / Period

PWM for Voltage Regulation

PWM signal, when used at different duty cycles, can provide varying output voltages. This method is used in several areas such as:

Switching regulators LED dimmers Audio Analog signal generation

Output voltage is regulated by averaging the PWM signal. The output voltage can be represented by the following equation:

Vout (Ton / Ttotal) * Vin

As you can see from the equation, the output voltage can be directly varied by adjusting the Ton value. If Ton is 0, Vout is also 0. If Ton is Ttotal (the full period), then Vout is Vin or the maximum possible output voltage.