12V - 7.29A ac/dc converter project Need Help

Discussion in 'The Projects Forum' started by Butterworth, Nov 6, 2011.

  1. Butterworth

    Thread Starter Active Member

    May 6, 2009
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    I got the info from here...

    Given the Vf is actually 1.42 not 1.2 as suspected before.
     
    Last edited: Nov 25, 2011
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Ahh, ok. I seem to have 20 or so threads going on; I jump around so much I can't remember all of the details for all of the threads.

    Somewhere about page 3, I had you measure your 12v 2a supply, and you mentioned that you measured 12.82v. Would you measure the voltage again, this time with a load on it? I want to see if the voltage changes with a load.
     
  3. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
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    Any load across it? I can use the regulator circuit I used for the LED tester.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    The way it's looking at the moment, if the supply comes down to 12v under load, then you can use 10 strings of 8 LEDs with ~6.3 Ohm resistors in each string to get ~100mA per LED. If the supply stays up at 12.82v, you'll need more like 15 Ohms per string.

    7 strings will have one of the 1.43v and 7 of the 1.42v LEDs
    2 strings will have eight of the 1.42v LEDs
    1 string will have the remaining LEDs.
    There will be 30mV difference between the highest and lowest Vf total.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, use the regulator circuit and an LED.
     
  6. Yako

    New Member

    Nov 24, 2011
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    Geez, you do well. No way I could do that.
     
  7. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
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    Excellent, I will report back in about 1.5 hours time with the result (Is not home from work yet)

    Don't worry, you will get there. I am good for maybe 1 thread at a time myself. :p
     
    Last edited: Nov 25, 2011
  8. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    OK, test resulted in stable voltage of 12.82V with load applied.
     
  9. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
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    BUMP!

    Sgt.Wookie, any word based on the above results? How do I add in the mosfet circuit to the array?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry, I'm rather distracted. Had a death in the family.
     
  11. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
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    Hey no worries, sorry to hear that. My condolences to you and yours.
     
  12. Butterworth

    Thread Starter Active Member

    May 6, 2009
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    BUMP, if anyone, can give me an idea for a PWM circuit to use in my project, please let me know, I am running out of creative juices trying to figure it out. Thanks.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry, I've been preoccupied.

    Have a look at the attached. Slight change of plans, but will still work with the things you have already.
     
  14. Butterworth

    Thread Starter Active Member

    May 6, 2009
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    Thank you for the update Sgt.Wookie.

    If I read this correctly, it only an on/off switch, will it not work with the Low/Off/Hi switch? My original plan was to use a hi & low power to be able to toggle between the two, in case the light is too "bright" for some locations.

    Also will any n-channel mosfet work? I do not recognize that model you noted.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Drat, I forgot all about the 3-way switch.

    Yes, that could be done. You want off, an adjustable dim, and full brightness, right?
     
  16. Butterworth

    Thread Starter Active Member

    May 6, 2009
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    Yes, I was thinking full brightness on "hi" and about 33% on "low" is that a good ratio?
     
  17. Audioguru

    Expert

    Dec 20, 2007
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    Your hearing's sensitivity to loudness and your vision's sensitivity to brightness are not linear (half the current seems to be half the output) but instead they are logarithmic so the range from very high to very low is very wide.
    Then half the power sounds only a little less and double the power sounds only a little more.
    Half the current in an LED is a little dimmer and double the current is a little brighter.

    10 times the power sounds twice as loud. 1/10th the power sounds half as loud.
    You can calculate the LED brightness yourself.

    33% of the current in an LED will make it appear dimmed a little. Try 10% instead.
     
  18. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    BUMP

    Sgt.Wookie, any word on the revision?
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry - there's a lot of people needing a lot of help; things tend to fall through the crack.

    Have a look at the attached. I didn't have a 3-position switch, so I used two SPDT switches. Don't let that throw you.

    You'll only have one common switch terminal; represented by the left side of S1a and S1b.

    The dim side is represented by S1a. When it is selected, the 555 timer runs, and the brightness is set via VR1.

    The bright side is represented by S1b. When it is selected, the 555 timer is prevented from running by R15 pulling up the base of Q1, which keeps C1 from charging, which keeps the output of the 555 timer high, which means the LEDs are on all the time.
     
  20. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    This looks awesome :) Thank you for the schematic!

    I see what you mean about the switch.

    There are zener diodes on the schematic after the switch? What V rating are they?

    Thanks again for this, it is very much appreciated!
     
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