dutycycle

Duty cycle is the fraction of time a periodic signal is in its active, or high, state during one cycle. It is commonly expressed as a percentage (0% to 100%) or as a unit interval between 0 and 1. For a waveform with period T, the duty cycle D is defined as D = ton / T, where ton is the duration of the high portion of the cycle.

In electronics, the term is closely associated with pulse-width modulation (PWM). In a PWM scheme, a fixed input voltage is applied to a load through a switching element that turns on and off each cycle. The duty cycle determines the average voltage or current delivered to the load: the average output is approximately Vin times D for a simple resistive load and a sufficiently fast switching frequency. Thus, changing the duty cycle modulates power without changing the switching frequency. A duty cycle of 0% yields no output, while 100% yields the maximum output; intermediate values produce proportional averages.

Common applications include motor speed control, LED dimming, switching power supplies, and audio amplification using switched-mode stages. In motors, the duty cycle affects average torque; in LEDs, it controls brightness. Practical limits include switching losses at high frequencies, nonlinearity or saturation in the load, and the need for filtering or energy storage to obtain smooth output.

Measurement of duty cycle can be done with an oscilloscope or digital meter by evaluating ton and the total period. The concept also appears in broader contexts to describe the proportion of time resources are allocated to tasks, but in electronics it most often relates to PWM and regulation.