High Frequency Led Modulation

At this frequency the driver drives from ground to 50 ma at full depth of modulation.

High frequency led modulation. To achieve high frequency dimming most led drivers have a pwm dimming input. Human eyes are incapable of noticing this flickering of light at high frequencies. For example to achieve a peak modulation current of 10 ma total is 25 ma requires a modulation input of vp 3v. Instead the human eye integrates the.

Pulse width modulation pwm with pwm as stated the led is turned off and on at the led s rated current at a high frequency. The photodiode is then placed in front of the leds so that its output is modulated from 0 to 1 v. For a fixed frequency switched mode power supply type led driver using a dc to dc conversion architecture the loop bandwidth is typically designed at or below 50khz. The idea i had was to create a constant current source most likely a simple circuit using an lm317 regulator then try and modulate the brightness of the leds.

Waveform lighting s flicker free led strip dimmer another reason we recommend a minimum of 25 000 hz is that pwm dimming can introduce a high pitched buzzing sound in power. Some people however are much more sensitive to flicker. As semiconductors leds can turn on and off up to a million times per second enabling the diodes to send data quickly says tom van den bussche founder of toric a lighting technology company based near paris. My goal is to be able to power some high power leds 1 amp each at a high frequency 30mhz or more for data communication.

To send data li fi relies on the modulation of light at frequencies that are imperceptible to the human eye in most lighting applications. To achieve a high led current modulation index in this configuration a large output voltage swing across ri is required and for operation at high frequency a very high slew rate op amp is needed. This frequency is not perceived by the human eye which usually sees anything that flickers faster than about 60hz 60 times per seconds as consistent. Furthermore this rapid switching is at speeds high enough for the human eye to see.

By utilizing a truly high frequency pwm dimming method even high frame rate and high shutter speed applications can be operated without any detrimental effects of flicker. The leds turn on when the current is high and turn off when the current is zero. Digital dimming switches the led on and off at a frequency higher than 300 hz. In this technique the frequency of the current is high enough to ensure that i the turning on and off of the leds are not apparent to the eye and ii it is outside the audible range to avoid any acoustic issues.

Finally frequency is increased and photodiode output modulation is monitored as an independent control of the driver s optical response. However the bandwidth of the led driver limits the dimming frequency and contrast ratio.