What's the difference between LED screen scanning
Author:Zhai Shijia Time:2021-06-10 09:12 Browse(986)
This is the average of the effective brightness. For example, LED is driven by 20 mA current pulse with 50% duty cycle, and its luminous effect is equivalent to driving by 10 Ma constant DC (100% duty cycle). In application
It is the average value of effective brightness.
for example.

What's the difference between LED screen scanning

LED is driven by 20mA current pulse with 50% duty cycle, and its luminous effect is equivalent to driving by 10mA constant DC (100% duty cycle).
in application
the duty cycle is usually 1:16 (6.25%).
theoretically.
the LED is driven in the mode of 1:16 (1 / 16 of the practical LED is on, and the other 15 / 16 of the practical LED is off), and the pulse current is lowHowever, in practical application, the pulse time of 1 / 16 is calculated according to the refresh rate of the whole screen and the technical parameters provided by the LED supplierIt is suggested that the maximum value of pulse current should be 5 times of the constant current value.
because the pulse current exceeds 50 Ma, its size is not directly proportional to the luminous brightness.
therefore, the brightness of the lamp should be improvedIt can still be close to the brightness of 20mA static driving.
the results show that the brightness of the system is still close to that of 20mA static drivingAdvantages of scan drivenThe biggest advantage of scan driver is to save driver chip.
make the driver circuit simple, so as to reduce the cost.
the design of scan driver is simpleDisadvantages of scan driverUsing large pulse current to get the required brightness.
make the light output decay faster than the LED without scanning drive.
the life of LED display is defined as normal operation until the white peak output value is the original valueHowever,
for the scanning drive system with a duty cycle of 1:8 or higher, its service life is greatly reduced(divided by 4), the brightness is only half of the factory value in about two yearsThe scanning driver accelerates the dimming of LED display screen.
the scanning driver is used to accelerate the dimming of LED display screenAnother problem is that the LED screen is still in the service life of the "mosaic" phenomenon, mosaic phenomenon is a disgusting phenomenonThis is due to the adoption of scanning driver.
each LED module is aging at a different rateCompared with the difference of adjacent pixels, the human eye is more sensitive to this effect.
the results show that the human eye is more sensitive to this effectIf different batches of LEDs are applied to one LED display screen, the situation may be even worse.
because the brightness of different batches of LEDs may also be inconsistent.
some LEDs must be improved during factory productionLine adjustment to make the LED of the whole screen match.
for those LEDs that are already dark, more current should be used to drive them.
this means that they will age faster in the future.
the light output of LEDs will increase with timeIn other words, in the early stage of normal use, the attenuation is faster.
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after years of production practice of LED display screen.
nowadays, scanning drive is widely used.
scanning drive uses the characteristics of human eye.
when LED is driven by high-frequency current pulse, scanning drive can reduce the power consumption of LED, For example,
LED is driven by 20 mA current pulse with 50% duty cycle, and its luminous effect is equivalent to driving by 10 Ma constant DC (100% duty cycle).
in application,
the duty cycle is usually 1:16 (6.25%).
theoretically,
LED is driven by 1:16 (1 / 16 of the practical LED is on), In addition, 15 / 16 of them are in the state of extinction,The pulse current is 16 times of the recommended constant current value, and the same brightness effect can be obtained.
however, in practical application,
the pulse time of 1 / 16 is calculated according to the refresh rate of the whole screen, and according to the technical parameters (the relationship between pulse current and pulse width) provided by the LED supplier, It is suggested that the maximum value of pulse current is 5 times of the constant current.
because the pulse current exceeds 50 Ma, its size is not directly proportional to the luminous brightness.
so the brightness can still be close to the brightness of 20 mA static driving.
the advantage of scanning driving is to save driving chip.
make the driving circuit simple, So as to reduce the cost.
the disadvantage of scanning driving is that the LED display adopts scanning driving mode.
if the maximum current limit is also followed, it will not appear any problem.
however.
the problem is gradually obvious, because the scanning driving LED uses large pulse current to get the required brightness, The lifetime of the LED display is defined as the time from normal operation to 50% of the original white peak value.
the lifetime of the LED display with non scanning driving is at least 70.
000 hours, that is, 8 years.
however.
for the scanning driving system with duty ratio of 1:8 or higher, its lifetime is greatly reduced (divided by 4), In about two years, the brightness is only half of the factory value.
the use of scanning driver accelerates the darkening of LED display screen.
another problem is that the LED screen still has "mosaic" phenomenon in its service life, which is a disgusting phenomenon,It makes the whole display screen look like it is made up of different LED modules, which has no overall feeling.
this is due to the adoption of scanning drive.
each LED module aging at different rates, resulting in rapid inconsistency, relative to the difference of adjacent pixels, The human eye is more sensitive to this effect.
if different batches of LEDs are applied to a LED display screen, the situation may be worse.
because the brightness of different batches of LEDs may also be inconsistent.
in factory production, some LEDs must be adjusted to match the LED of the whole screen.
for those LEDs that are dark, they need to be driven by a larger current.
means that it is necessary to adjust the brightness of LEDs The light output of LED decays logarithmically with time.
that is to say, it decays faster in the early stage of normal use.
LED displays produced in different batches are used.
scanning driving mode is adopted, Mosaic phenomenon may appear in less than a year.
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powerful network functions.
support all kinds of video (AVI.
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