how does your computer put on such a fantastic light show with all those LEDs
how do the lights fade and change colors is there a legion of pixies with an
amazing array of dimmer switches coordinated precisely so that your
friends are impressed with your RGB lighting well the reality is a bit less
Fantastical but with the recent unionization of pixies we have the much
more practical pulse width modulation so
what is pulse width modulation pwm varies the perceived power going to an
electronic device by very quickly turning the power on and off the
perceived output is changed by varying the duty cycle now the duty cycle isn't
the time it takes your dog to spin around before going about its business
but instead how long the signal is turned on versus turned off this means
with the duty cycle of 50% the signal is turned on half the time and off the
other half whereas a duty cycle of 100%
means the signal is always on an important part of the duty cycle is the
switching frequency or how fast the signal is turned on and off for instance
turning an LED on for a second and then off for a second would be a duty cycle
of 50% but the LED won't be half as
bright it'll just be annoying to make
the LED appear dimmer the onoff switching has to be faster than the
flicker Fusion rate or how quickly a
light has to turn on and off to be perceived by the brain as being
continuously on in humans the flicker Fusion rate is around 18 times per
second typically LEDs control by pwm will be switched on and off over a 100
times per second or 100 Hertz by using a duty cycle of 25% at 100 HZ it means
that the LED would be turned on and off 100 times per second but the duration of
each on cycle is only a quarter of the time making the LED appear 25% as bright
and and as you probably know pwm is also useful for quiet and efficient PC
cooling older fans controlled from the motherboard had very poor speed control
meaning that the fans would run much faster and louder than they actually
needed to be at that point in time pwm fans however allow for the motherboard
to easily control the fan speed giving low quiet fan speeds when just browsing
the web to gale force wins when you're
playing crisis so can we dim a light or change a fan Speed without using pwm
well older systems might use DC voltage control this works by changing the
resistance in a circuit the more resistance the less power transmitted to
the fan or light since there is no
switching DC control has the advantage of smoother power delivery but they
often don't offer the same range of speeds that a pwm fan does not to
mention that any power that isn't being used gets wasted as heat which is why
old dimmer switches use the same amount of power no matter how much light they
made it has been said that pwm monitors can cause eye strain from the constant
flickering although makers of DC controlled monitors seem to pretty much
be the only ones that are saying this so
trust them if you want beyond changing how much power is going to something pwm
can be used to transmit data between two devices where pulses of different
lengths represent the data being transferred this is how your TV remote
switches channels and how data is transmitted from cell towers to your
phone pwm is also used in some audio amplifiers making them extremely
efficient the typical efficiency of a non pwm amplifier is between 25% and 50%
while a pwm amp can reach efficiencies of
99% the cool operation and high efficiency makes these amplifiers
popular in car audio you can bump t-swift all day without you know turning
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