problem with rise and fall time of LED

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how to reduce rise and fall time of led??
I am getting problem with this as when using PWM for intensity change rise and fall time come in picture.
So Color temperature of led get changed.
so what is solution to reduce rise and fall time of led.
or is there any different method??
 

What's your switching frequency? Up to several tens of MHz you shouldn't get rise/fall time problems. Did you measure these time values?

Color changes a minor little bit with temperature, which may depend on PWM factor in case of medium/high power drive.
 

Here is a method for sharpening the corners of square waves, which I saw in my oscilloscope adjustment instructions.

A capacitor in series alone has the effect of generating a spike. By adding a resistance across it, you allow some of the incoming waveform to bypass it.



The first capacitor represents invisible 'stray capacitance', which causes the incoming square wave to have soft transitions. (Labelled as Out 1).

Component values are an example in order to illustrate the concept. You must select values which will work with your circuit, and operating frequency.
 
You may be driving it too hard. What is the colour What is the supply voltage and what is the current-limiter resistance.
 

I think this may be more about the DC-DC output filter
than the switching waveform. We'd need to be shown a
schematic to conclude anything of that sort.
 

You didn't tell about the used LED type, but the term color temperature suggests a white LED.

Change of color temperature with LED current is a known phenomenon, I would also expect different response times of different lumiscence colors utilized in a white LED. This could cause an effective color shift with high frequent PWM.
 

i am using cree xp-g2 led. i have not observed but while studying about factor affecting color temperature i saw that edges.
that is rise and fall time so there is linearly changing current so at different current there is different color temperature.and it will repeat continously. so there will affect color temperature.
is there any ic from texas ??
bcoz i was saw ones but forget it..
 

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