Do LEDs have a "Favourite" Operating Frequency?

Discussion in 'The Projects Forum' started by Tom Kay, Feb 23, 2009.

  1. Tom Kay

    Thread Starter Active Member

    Feb 10, 2009
    35
    0
    Hi;
    I know that LEDs can handle rapid on/off pulsing, and hence they respond well to a PWM dimmer. I read that they also could be cycled very rapidly, but what I am not sure about is the optimum operating frequency (if they even have one).

    Back to Ebay for a second, I am considering the purchase of a PWM circuit that outputs 80 watts at 12 to 40 VDC. The duty cycle is adjustable from 0 to 100%. The operating frequency is pre-set at 30Khz, although maybe adjusting the frequency is just a case of swapping a resistor on the board, and maybe a cap.

    Does this seem like an acceptable freq for LEDs to be fed with? It's well above 1Khz, so my eyes sure won't see any flickering. Is there a better frequency for the modern bright, 5 mm, warm white LEDs with a FV of 3.4 vdc, and a typical current draw?

    Thanks, Tom.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    I would say not, but at very high frequencies the internal capacity of the led may distort the PWM signal.

    Greetings,
    Bertus
     
  3. Tom Kay

    Thread Starter Active Member

    Feb 10, 2009
    35
    0
    Hi Bertus;

    Thanks for the help. I'd still be curious if 30Khz is acceptable for LED pulsing.

    Any idea?

    Cheers, Tom.
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    The infrared LED used for remote control mostly operates on 38KHz pulsing frequency.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    L. Chung brings up a very good point; if your purpose is remote control via IR LEDs, many of them operate in the range of 37kHz to 40kHz, most around 38kHz.

    If your application is purely in the visible light spectrum, you don't need to worry about it; anything above 1kHz won't be visible to the human eye.
     
  6. Tom Kay

    Thread Starter Active Member

    Feb 10, 2009
    35
    0
    L. Chung and SGT Wookie;

    Thanks for the info. That's helpful. I guess it means that the 30Khz units should work fine for dimming purposes without messing up my IR controlled stuff.

    Cheers, Tom.
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Hard to tell as 30KHz is very close to 38KHz.

    When the LED is ON, you could end up reducing the sensitivity of other IR controlled stuff by a large amount. Most IR modules can detect this 30KHz signal or even try to decode it.

    Better seek clarification/confirmation from the seller or any previous user.
     
Loading...