PWM circuit, want more leds.

Discussion in 'The Projects Forum' started by ihod, Feb 4, 2010.

  1. ihod

    Thread Starter New Member

    Feb 4, 2010
    6
    0
    Hello,

    Read through the entire thread hoping there would be a schematic somewhere. I built a pwm module that works good for a few led's but i would like some input if at all possible on beefing it up so it can drive more led's. I cant find much information on the net which is strange.

    This is my current schematic/parts list:
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    You have hyjacked an old thread.
    I moved it to its own thread.
    This is the thread I have taken it off : http://forum.allaboutcircuits.com/showthread.php?t=7533
    Please start a new thread when you have questions.
    you can always refer to the older thread.

    Greetings,
    Bertus
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Not such a good design.

    The 555 timer already has a Darlington follower output for the high side; meaning that at even light loads, the output is about 1.3v less than Vcc. That design ads yet another Darlington follower, so subtract another 1.3v from Vcc.

    You would get better results using the 555 to switch the low side (ground side) of the LEDs using an N-channel power MOSFET.

    Make certain that the maximum LED current is controlled via resistors, or you will rapidly burn them up.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    What is the voltage of the system? This dictates drivers. We have quite a few good schematics on this site, but we need more info.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    On 2nd look, it appears that this is an automotive application for brake/turn signal lights.

    We're kind of trying to get out of that business, as such modifications are becoming illegal in some countries. Apparently, quite a few experimenters have ruined it for everyone else.
     
  6. ihod

    Thread Starter New Member

    Feb 4, 2010
    6
    0
    OK, i finally built it, used 15a pnp transistors, and beefed up the diodes on the brake/park incoming line. She works but blinks like a strobe and there isnt alot of difference between park and brake. I know that the rate of the pulsing is controlled by the 12k and 1k resistors so im wondering if maybe i need to change those around a little, i just dont know which way to go, up or down in ohms. The 555 got really hot at 16v (testing on a transformer) so im guessing im going to need a small ram heatsink for the 14v that its going to be pushing.

    SgtWookie, im very new to all this so if you could explain a little about what the mosfet would do it would be greatly appreciated.

    Thanks
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    If you have already installed this circuit in a motor vehicle, you need to remove it, and restore the brake/parking lights and wiring to the original manufacturer's specifications.

    If you have not installed it, then good.

    We do not have the means to ensure that components you have selected will meet the Department of Transportation regulations regarding motor vehicle lighting when installed, nor any way to check that your quality of workmanship is adequate to be reasonably certain that the lights will function properly over the lifetime of the vehicle.

    This is most definitely a safety issue. I am giving you the best advice that I can to ensure your continued safety.
     
  8. ihod

    Thread Starter New Member

    Feb 4, 2010
    6
    0
    Just testing for now, I would never install a blinking light in my car, I drive a saab, it would be an insult to rice it out :)

    I ultimately want a decent dual brightness tail solution and if I keep messing with this pwm I shall eventually master it. As for now, I have converted the third brakelight to 50 led's and changed the reverse lights to 3W Luxeon Star Emitters (5 in each light).
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,765
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