are there Ultra High PWM frequency LED drivers

Discussion in 'General Electronics Chat' started by renl, Jun 23, 2010.

  1. renl

    Thread Starter New Member

    Jun 23, 2010
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    Hi, I was wondering if there are any LED driver that is able to drive the PWM frequency in the 100kHz to 500kHz range?

    Secondly, it seems that LED datasheet don't spec in the frequency response. I wonder wondering if LEDs might act as a "filter" such that PWM signals of the above mentioned range becomes ineffective at the LED.

    Thanks. [​IMG]
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, there are dedicated ICs for driving LEDs using frequencies in the 200kHz-1MHz range. They just need an inductor, a cap, and a resistor or two.

    No, the LED's frequency is in the visible spectrum. The wavelength of light is measured in nanometers. The wavelength of a 100MHz signal is roughly 3 meters.
     
  3. renl

    Thread Starter New Member

    Jun 23, 2010
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    Do you know of any particular part number that is able to drive the LED pwm at 200kHz to 1Mhz range?

    I didnt mean driving the LEDs so fast that it surpass the wavelength of light. However has any ever measured actual light output with a light detector wired to an oscilloscope? Does the light output correlate 100% to the input signal or maybe the generation of photons is slightly "capacitative" in nature?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I don't even know where you are. I could give you a part number, and you wouldn't be able to find it in your area, or it wouldn't be appropriate for your application - as all you've mentioned is LEDs. I have no clue what your requirements are beyond that.

    However, you could go on Digikey.com or another supplier's website, and type in PMIC LED driver, and then start narrowing down your selection from there.

    There are thousands of different types of these regulators on the market.

    Try clicking here: http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556628&k=PMIC LED Drivers

    As far as your 2nd question - the color of light may change if you get near the maximum current of the LED. If that happens, it's likely the LED is permanently damaged.

    Switched-inductor LED drivers are pretty efficient, and the current remains quite steady; within a few percent. You might be able to detect the difference in light, but you would need an instrument with extremely high bandwidth.
     
    Last edited: Jun 24, 2010
  5. renl

    Thread Starter New Member

    Jun 23, 2010
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    Thanks, I'll take a look in digikey.

    However I suspect we might be talking about a different aspect of the LED driver. I understand the switching frequency of an LED driver can be very high but that is to regulate the constant current that is desired.

    What I was enquiring was about pulse width modulation to dim the light output of up to 5 or 10% duty cycle.

    Why I was asking about this is because when I was looking around the internet, when they advertise about ultra high pwm frequency LED illumination, the frequency is only at 100kHz. And when I was looking around at LED drivers, when they say its ultra high frequency, their switching frequency is very high, but their PWM frequency is usually up to 50kHz only.

    Again all this orginated when I read an article about high speed cameras seeing a flickering image when used with LED illumination. So it seems LED illumination technology is not really keeping up with the speed at which some cameras are going at.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Ahh, I see. You had not mentioned photography before now.

    If you look on Digikey, you will indeed find some very fast-switching drivers.
     
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