SVS-Vistek SHR 10GigE, Manual

Page: 73 / 103

5.3.3 PWM
During Pulse Width Modulation (PWM), a duty cycle is modulated by a fixed fre-
quency square wave. This describes the ratio of ON to OFF as duty factor or duty
ratio.
Why PWM?
Pulse width modulation is an extremely efficient way (in terms of power dis-
sipation) to provide/regulate electrical power to consumers as long as they do not
need uninterrupted supply (such as diodes or LEDs). The interruption times might
be as short as nano seconds.
LED characteristics
Since LEDs have a bounded workspace, the PWM ensures a variable intensity of
illumination at a constant current on the diodes. The constant current guarantees
a linear light emission response curve of the LED from 0-100% PWM intensity.
Running LED lighting in flash mode will increase LED lifetime because of reduced
LED heat dissipation.
Implementation of PWM
The basic frequency of the modulation is defined by the cycle duration "T".
Duty cyle "T" is written into the registry by multiple of the inverse of camera fre-
quency in 15 ns steps (refer to
"System clock frequency" on page 63 ).
The intensity of a PWM
The duty ratio is calculated as: Δ% = t / T. It is written above the value of "t" as
PWMChange0-3[SeqSelector] per sequence into the registry.
PWMChange0-3[SeqSelector] unit is percentage value.
5 Feature description 73