# Duty cycle

The duty cycle (also drive level , English duty cycle ) are of a periodic sequence of pulses according to standardization , the ratio of pulse duration to the period of. The duty cycle is specified as a ratio of the number dimension with a range of values ​​from 0 to 1 or 0 to 100%. This is explained below using ideal pulses that form a square wave . The following applies to the duty cycle${\ displaystyle D}$

Time course of a square wave signal : equivalency ; : RMS value
${\ displaystyle y _ {-}}$${\ displaystyle y _ {\ mathrm {eff}}}$
${\ displaystyle D = {\ frac {\ tau} {T}}}$
 ${\ displaystyle \ tau}$ : Pulse duration ${\ displaystyle T}$ : Period duration

A symmetrical pulse is created especially for . ${\ displaystyle D = 0 {,} 5 = 50 \; \%}$

The term pulse duty factor does not appear in the standards mentioned and is not used uniformly in the literature; it is used both for the duty cycle and its reciprocal value as well as for the ratio between pulse duration and pulse spacing. The last variant corresponds to the no longer standardized term on -off ratio , i.e. the ratio with a value range from 0 to . ${\ displaystyle {\ frac {\ tau} {T- \ tau}}}$${\ displaystyle \ infty}$

## Application and meaning

Frequency spectrum depending on the duty cycle

The equivalent value of the electrical voltage can be changed by varying the duty cycle . Since this setting occurs with almost no power loss due to the switching - in contrast to the setting with a series resistor  - this digital method is a widely used method for controlling electrical voltage and power . Applications are switched-mode power supplies and vibration package control for heating.

The underlying pulse width modulation is also a type of modulation for generating continuously adjustable DC voltage , in which the demodulation leads to averaging through a low-pass filter behind the pulse-width modulating circuit. In spite of the on-off switching, an analog signal is generated , since the duty cycle is a continuously adjustable variable. In the case of sufficiently sluggish applications, the low-pass filter is dispensed with because the sluggishness of the system alone is sufficient for averaging, for example with heating.

Some digital-to-analog converters also work with an adjustable duty cycle. In the case of a square-wave voltage with a constant period, the digital input information determines the pulse width that can be set in steps in this case and thus the average output voltage proportional to it.

With phase control , motor speeds are set using a variable duty cycle on a sinusoidal voltage.
The same applies to the chopper control .

## Individual evidence

1. DIN 5483-1: 1983-06 Time- dependent quantities - naming the time-dependency
2. DIN EN 60469: 2014-02 Transitions, impulses and associated vibration maps - terms, definitions and algorithms
3. Klaus Beuth, Wolfgang Schmusch: basic circuits . 13th edition. Vogel reference book, Würzburg 1998, ISBN 3-8023-1733-5 .
4. Brechmann, Dzieia, Hörnemann, Pretty, Jagla, Petersen: Electrical Tables communication technology . 3. Edition. Westermann, Braunschweig 2001, ISBN 3-14-225037-9 .
5. Dietmar Benda: How do you measure with an oscilloscope? Franzis, 2007, ISBN 978-3-7723-6766-3 .