Duty Cycle Calculator

What is a Duty Cycle?

Duty cycle is a term used to describe the proportion of time that a system or signal is in an active state as a percentage of the total time under consideration. In simpler terms, it represents how long a signal is "ON" compared to its total period.

Where:

• ON Time (pulse width): The duration when the signal is active (high)
• Period: The total time of one complete cycle (ON time + OFF time)
• Duty Cycle: Expressed as a percentage between 0% and 100%

Common Duty Cycle Examples

• 0% Duty Cycle:

  Signal is always OFF (low state)

• 25% Duty Cycle:

  Signal is ON for 25% of the period and OFF for 75%

• 50% Duty Cycle:

  Signal is ON for half the time and OFF for half the time (equal ON and OFF periods)

• 75% Duty Cycle:

  Signal is ON for 75% of the period and OFF for 25%

• 100% Duty Cycle:

  Signal is always ON (high state)

Applications of Duty Cycle

Pulse Width Modulation (PWM)

PWM is one of the most common applications of duty cycle. By varying the duty cycle of a PWM signal, you can control the average power delivered to a load. This technique is used in:

• Motor speed control
• LED brightness dimming
• Heater temperature control
• Audio amplification in Class-D amplifiers
• Switch-mode power supplies

Digital Communications

Duty cycle is important in digital signals:

• In serial communications, signals often need a specific duty cycle for proper data transmission
• Clock signals typically use a 50% duty cycle for synchronization
• Pulse position modulation encodes data by varying the duty cycle

Industrial Equipment

In industrial settings, duty cycle refers to the operating cycle of machines:

• Welding machines are rated by duty cycle (e.g., a 60% duty cycle at 300A means the welder can operate continuously for 6 minutes out of every 10 minutes at 300 amperes)
• Motors and other equipment have duty cycle ratings that specify how long they can operate before needing to cool down

Relationship Between Duty Cycle and Average Voltage

In PWM applications, the average voltage delivered to a load is directly proportional to the duty cycle:

For example, if you have a 12V supply and set the PWM to a 25% duty cycle, the average voltage delivered will be 3V (12V × 0.25).

This relationship allows precise control of power delivery without the efficiency losses associated with linear regulation methods.

Duty Cycle and Frequency

Duty cycle and frequency are related but different concepts:

• Frequency: Measures how many complete cycles occur per second (measured in Hz)
• Period: The time duration of one complete cycle (T = 1/f)
• Duty Cycle: The ratio of ON time to the period

You can have signals with the same duty cycle but different frequencies, or signals with the same frequency but different duty cycles.

Measuring and Setting Duty Cycle

Duty cycle can be measured using:

• Oscilloscopes with duty cycle measurement functions
• Multimeters with duty cycle measurement capabilities
• Specialized frequency counters

In microcontrollers and digital systems, duty cycle is typically set using:

• PWM hardware modules with configurable duty cycle registers
• Software timing loops that control GPIO pins
• Specialized PWM controller ICs