Pls help me for this issue

Discussion in 'The Projects Forum' started by s.dineshkumarece, Dec 16, 2010.

  1. s.dineshkumarece

    Thread Starter New Member

    Apr 2, 2010
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    Dear all,

    Pls help me out of this issue attached, in the below attachment LD1, LD2,LD3,LD4 are red and LD5, LD6 are white, this circuit will be interfaced to our spl board were we control the operation using the switch in this board.
    1) when the sw1 is pressed reds light should be ON and white should be in off state completely
    2) when the sw2 is pressed white should be ON and the red should be go off completely.

    But in our board the red light is not get completely off it glowing slightly, pls help me to get off completely. Pls give me reply in quick, my mail id is <SNIP> ....
    V+ - 6.3 volt
     
    Last edited by a moderator: Dec 16, 2010
  2. Wendy

    Moderator

    Mar 24, 2008
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    The thing you have missed is the current going through the base emitter resistor on the other side. If you really need the LEDs to go completely dark you will need to use something else other than transistors, other wise you will have to put up with the 0.2ma or so of current through R3 or R4 (you didn't mention power supply voltage). Have you considered using a 4001 or some other CMOS chip?

    [​IMG]
     
  3. s.dineshkumarece

    Thread Starter New Member

    Apr 2, 2010
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    The transistor used id 2N2222A, and the voltage is 6.3Volts
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    You will not be able to use two white LEDs in series then, since their drop is between 3.4-3.6VDC. Here is another alternative to CMOS (I prefer the CMOS solution). How married are you to 4 LEDs on the one side?

    [​IMG]

    R1 and R2 can be much higher resistance, say 1KΩ. If I have time I'll draw the CMOS version...
     
  5. s.dineshkumarece

    Thread Starter New Member

    Apr 2, 2010
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    Thank you sir, whether its possible to do something with the old circuit, since we made more than 500 pcbs with that... if it possible to add some components n do the change
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    The first design is doing something with the old circuit. You should have breadboarded a version before starting production, the original print has many, many rookie mistakes, such as putting LEDs in series that add up to more than the power supply, or putting LEDs in parallel to each other, or not calculating where all the current paths are. Here is the CMOS version, you can use it or not, as you please.

    [​IMG]

    I have what might be an idea, be right back...
     
  7. s.dineshkumarece

    Thread Starter New Member

    Apr 2, 2010
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    many thank you for your support....
     
  8. Wendy

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    Mar 24, 2008
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    OK, Look at this, the indicators LEDs will be reversed, but will go completely out.

    [​IMG]
     
  9. Wendy

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    Mar 24, 2008
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    Occurred to me that one of my diagrams was off...

    [​IMG]

    Wonder if the OP will be back?
     
  10. wayneh

    Expert

    Sep 9, 2010
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    If I was a betting man, I'd wager "no". He's too busy reworking 500 PCBs.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    Think the idea in post #8 might work? The LEDs won't be fully powered, but it would do the job.

    Who in his right mind makes 500 PCBs without building one prototype?
     
  12. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    OUR new members. :)
     
  13. wayneh

    Expert

    Sep 9, 2010
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    I think it would work, but might draw more current while "off" than the original design. Small price to pay.
     
  14. CDRIVE

    Senior Member

    Jul 1, 2008
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    Nothing is going to rectify your mistake of paralleling those LEDs without doing a complete re-board but your issue of the LEDs not Completely turning off may be corrected by using these very low Vgs Fets. You would have shunt both sets of LEDs with high val resistors to insure the Gates get 5V. Odds are, these Fets will turn the Leds fully on with as little as 3.5V - 4V to the gates.
    http://parts.digikey.com/ca/1/529051-mosfet-n-ch-60v-1-7a-4-dip-irld014pbf.html
     
  15. s.dineshkumarece

    Thread Starter New Member

    Apr 2, 2010
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    ya correct wayneh
     
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