What is the Duty Cycle?

The Duty cycle is the ratio of time on a circuit when the load is ON compared to the time when the load is OFF.


we can say that “the Duty cycle is the measure of the system’s active time”. Basically, it is measured in percentage (%) that what percent of the load is ON compared to OFF-load.

The Formula of Duty Cycle:

formula of duty cycle

  • Where D is the duty cycle,
  • PW is the pulse width (pulse on or active time)
  • T is the total period of the signal.

Explanation of Duty Cycle:

If a digital signal spends its half of the time ON and the other half OFF, then the digital signal has the duty-cycle of 50%. If the percentage is higher than 50%, the digital signal spends more time in the high state than the low state and vice versa if the duty cycle is less than 50%.

More the duty cycle percentage (%) betters the system operation.

For example: if the duty cycle is 40% it means the load is ON for 40% of the time and OFF for 60% of Time.

 

Here is a figure that illustrates better about duty cycle:

duty cycle example

  • 50% of Duty-Cycle indicates that the system is active for 1/2 times.
  • 25% of Duty-Cycle indicates that the system is active for 1/4 times.
  • 75% of Duty-Cycle indicates that the system is active for 3/4 times.

How to Calculate Duty Cycle:

The duty cycle of a signal measures the fraction of time that a given transmitter transmits this signal. This fraction of the time determines the total power transmitted by the signal. Signals with longer duty cycles carry more power.

This makes the signal stronger, more reliable, and easily detectable by receiving equipment. Signals with longer duty cycles require less efficient receivers than signals with shorter duty cycles.

Measure the pulse width of the transmitted signal. If you do not know this, connect the signal output to the oscilloscope input. The oscilloscope screen will show a series of pulses oscillating with the frequency of the signal. Note the width in seconds or microseconds of each pulse. This is the pulse width or PW signal.

Calculate the period, or “T”, frequency, or “f” using the formula: T = 1 / f.

For example, if the frequency is 20 Hz, then T = 1/20 with a result of 0.05 seconds.

Calculate the duty cycle, represented by “D,” through the formula D = PW/T.

For example, if PW is 0.02 seconds and T is 0.05 seconds, then D = 0.02 / 0.05 = 0.4 or 40%.

 

Example of duty cycle

In an automotive electronic fuel injection system, voltage pulses supplied to the fuel injector valve solenoid control the fuel injector valve at a fixed rate of 10 cycles per second, or 10 Hz.

Pulse width modulation allows fuel supplied to the engine to be precisely controlled electronically. The voltage average for each duty cycle is determined by the amount of pulse ON time.

Duty cycled solenoids use a variable duty cycle signal to vary flow or adjust pressure. The longer a solenoid remains open, the more flow and less pressure develops. These solenoids are either feed-controlled or ground-controlled.

Duty Cycle in Electronics:

In Digital Electronics, signals are represented by logic levels of 1 and 0. Logic 1 stands for the presence of an electric signal and 0 in the absence of an electric signal.

For Example:

A Digital signal has a square output (10101010) then the duty cycle for this signal will 50% because the pulse remains high for almost half (1/2) of the period and low for another half (1/2) of the period. Almost every component and system has its own duty cycle value which indicates that it will be operated up to this value of duty-cycle.

Duty Cycle in Electrical:

Electrical Components uses very less duty-cycle to operate as compared to Electronic Components.

   For Example:

Electrical motors use very less duty-cycle. if a motor runs for one out of 200 seconds or 1/200 of the time, then, its duty cycle is 1/200, or 0.5 per cent.

 

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