shorting one led from two in serie- Mtbr.com
Results 1 to 14 of 14
  1. #1
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    270

    shorting one led from two in serie

    Hello,

    I am thinking on making a light with two or more leds in series and adjusting brightness using switch(-es) which are short circuiting some leds. The question is: will a driver adjust the power quick enough not to burn other led?
    Attached Images Attached Images

  2. #2
    mtbr member
    Reputation: znomit's Avatar
    Join Date
    Dec 2007
    Posts
    1,980
    Quote Originally Posted by Itess
    Hello,

    I am thinking on making a light with two or more leds in series and adjusting brightness using switch(-es) which are short circuiting some leds. The question is: will a driver adjust the power quick enough not to burn other led?
    No. You will destroy led2.

    If you want dimming use a driver that halves the current.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    270
    Quote Originally Posted by znomit
    No. You will destroy led2.

    If you want dimming use a driver that halves the current.
    Thanks for the warning. I was afraid of that. I want to switch not only dimming, but light configuration also.

  4. #4
    mtbr member
    Reputation:
    Join Date
    Sep 2007
    Posts
    453
    It is possible ONLY if you switch off the light completely.

  5. #5
    mtbr member
    Reputation: znomit's Avatar
    Join Date
    Dec 2007
    Posts
    1,980
    Quote Originally Posted by zemike
    It is possible ONLY if you switch off the light completely.
    Good idea.

    A four pole on/off/on will do this for you

  6. #6
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    270
    Quote Originally Posted by zemike
    It is possible ONLY if you switch off the light completely.
    Interesting. Now I am thinking of some way to shutdown the driver when pressing the switch.

  7. #7

    Reputation:
    Join Date
    Mar 2009
    Posts
    16
    A driver with dimming capability is the only way you're going to manage this. Most LED drivers use current mode control, so if you have a 1A driver, it will source 1A of current to the LEDs. Let's say your LEDs have a forward voltage drop of 3V at 1A. If you closed that switch, 6V would appear across LED2 briefly, and would cause it to fail.

    If you wanted to achieve the same effect without blowing up the LED, you could parallel the LEDs and then open circuit one of them. However, each LED would then be getting 500mA with both connected, and when you opened the switch, the current in LED2 would increase to 1A (with the assumed 1A driver).

    If you went with the parallel configuration, and simultaneously halved the output current of the driver, then you'd get the desired effect.

  8. #8
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    270
    Quote Originally Posted by shinkansen
    A driver with dimming capability is the only way you're going to manage this. Most LED drivers use current mode control, so if you have a 1A driver, it will source 1A of current to the LEDs. Let's say your LEDs have a forward voltage drop of 3V at 1A. If you closed that switch, 6V would appear across LED2 briefly, and would cause it to fail.
    Yes, I thought about that, that's why I asked.
    If you wanted to achieve the same effect without blowing up the LED, you could parallel the LEDs and then open circuit one of them. However, each LED would then be getting 500mA with both connected, and when you opened the switch, the current in LED2 would increase to 1A (with the assumed 1A driver).

    If you went with the parallel configuration, and simultaneously halved the output current of the driver, then you'd get the desired effect.
    Actually, I was thinking of 3-4 leds with differen optics with 2-3 switches.Now I think it's possible with a very custom driver for which I don't have the knowlege. I have to think of something else.

  9. #9

    Reputation:
    Join Date
    Mar 2009
    Posts
    16
    You could go with several small micropuck drivers (http://ledsupply.com/micropuck.php) and just switch them on and off individually. A guide for a light using these drivers is at http://www.racedaynutrition.com/Features/bikelight.aspx; you may have already seen it.

  10. #10
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    270
    Quote Originally Posted by shinkansen
    You could go with several small micropuck drivers (http://ledsupply.com/micropuck.php) and just switch them on and off individually. A guide for a light using these drivers is at http://www.racedaynutrition.com/Features/bikelight.aspx; you may have already seen it.
    Well, yes, I thought about several drivers. I saw several drivers efficiency diagramms, and usually with 2-3 leds drivers are more effective than with one. And it's pretty critical to me because 4 XP-E with 4 drivers with 80% efficiency will reduce runtime and heat the environment more as with one driver and 95% efficiency.

  11. #11

    Reputation:
    Join Date
    Mar 2009
    Posts
    16
    The micropuck is fairly efficient in buck mode, with an efficiency of around 90% between 4 and 5.5V input. I agree with you though, it's not an elegant solution and certainly not the best.

  12. #12
    mtbr member
    Reputation:
    Join Date
    Feb 2009
    Posts
    270
    Quote Originally Posted by shinkansen
    The micropuck is fairly efficient in buck mode, with an efficiency of around 90% between 4 and 5.5V input. I agree with you though, it's not an elegant solution and certainly not the best.
    MicroPuck Online Data Sheet does not agree with you

    Yes, multiple micropuck drivers aren't best and certanly not elegant solution. But thanks for bringing this up, it was a fun to think a little bit more in this way.

  13. #13

    Reputation:
    Join Date
    Mar 2009
    Posts
    16
    You'll need to read the application notes for the buck mode characteristic - http://ledsupply.com/docs/MicroPuck-Applications.pdf

    I'll let you know if I think of anything else

  14. #14
    mtbr member
    Reputation: znomit's Avatar
    Join Date
    Dec 2007
    Posts
    1,980
    Quote Originally Posted by Itess
    Well, yes, I thought about several drivers. I saw several drivers efficiency diagramms, and usually with 2-3 leds drivers are more effective than with one. And it's pretty critical to me because 4 XP-E with 4 drivers with 80% efficiency will reduce runtime and heat the environment more as with one driver and 95% efficiency.
    Its not just driver efficiency, its LED efficiency too. LEDs are much more efficient at low currents.
    ie running 1 led at 1A is much worse than running 4 at 250mA... 50% more efficient

    The only reason to switch individual leds is if you want different beam patterns.
    Here I use a flood and a spot

Members who have read this thread: 0

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2020 VerticalScope Inc. All rights reserved.