Voltage controlled switch

Discussion in 'Homework Help' started by Handjolyna, Jul 25, 2007.

  1. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
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    Voltage controlled switch



    I need a simple circuit that will allow only the 10 volts and up, to actived a relay, when the input is more than 10 volts . The circuit is used to drive a 12v relay.
    This is for a car for the (day runing light) Hi beam to instale hid xenon I don't whant they comme on when is 7 volts.
    Thanks for any help you can give.
     
  2. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
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    0
    Do a zener diode can do it??
     
  3. lightingman

    Senior Member

    Apr 19, 2007
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    22
    Hi,You can do this with 1 IC... LM311 comparator. It can drive small relay direct (up to 50mA), or with a transistor, larger relays.....Give me a day or so, and I will post the schematics....Daniel.
     
  4. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
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    Thank-you Daniel for your answser, I'll whait for your schematics I whant to drive a 12v car relay.
     
  5. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    O.K..... No problem...Daniel.
     
  6. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Why not using an LM393 comparator with a PNP transistor? The LM311 needs a dual supply and is more complicated to use.
     
  7. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    Hi...The LM311 is designed for dual or single rail, it will only require a dual rail if you are trying to detect levels near zero volts....The LM311 has an NPN output transistor that can be used for low or high side driving.... A car relay requires about 200 to 300mA, so an extra transistor (PNP for high side driving) or (NPN for low side driving).....So 1 x LM311, 6 x resistors, 1 x pre-set, 1 transistor and 1 x diode... and that's it....Daniel.
     
  8. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    O.K...I just want to clarify a couple of things now...Are you saying that you want the relay to come on when the voltage is 10 volts or higher, and then off when the voltage goes down to 7 volts, or lower ?.....If this is the case then It will need to detect 2 seperate levels (the upper 10 volts) and (the lower 7 volts)..... This would require 2 comparators and an R/S latch.....I feel that the easiest way to do it would be to use a PIC12FXXX (8 pin)microcontroller to read the input voltage, and then compare it with 2 other inputs (a pre-set on each one to set the limits)... This would then give you the 1 output to drive a transistor to switch the relay from 2 user pre-set levels.....This may sound complex, but it is quite a simple program to write, if you can wait until Sunday when I am back in the workshop, I can write and program a PIC to do this.....(if that is the way you wish to go)...The PIC's are only about 1GBP to buy, take up little space and are very low power...I would have no problem sending you the PIC and all the schematics...Just P.M. me your details....Daniel.
     
  9. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
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    No, I just want the relay to come on when the voltage is and 10 volts or higher, and then off when the voltage is lower 10 volts.
    Thank-you.
     
  10. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    O.K....It is done....I have done a prototype and it works well.... Will do the schematics tonight and post tomorrow afternoon......Daniel.
     
  11. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
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    Nice I'll wait
     
  12. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    O.K..... Here it is I have tried this, and it works fine.....
    If you have any problems, just let me know and I will sort them out....


    Good luck....

    Daniel.
     
  13. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
    8
    0
    Thank-you very much I gona try it I thought it will be more simple than this graphic, you work like a pro.
     
  14. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
    8
    0
    I am not a pro in graphic, what is a T.P?
    and (4u7 10v) do it mean 4700UF 10 VOLTS??
    Do you have a picture of your test unit?
     
  15. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    T.P. is shown on the schematic (T.P. = test point)...4u7 = 4.7uF at 10 working volts....on the resistors R = Ohms, 4K7 would be 4.7K Ohms....5V1 on the zeners is 5.1 volts...Do you want to build this on matrix board, vero (strip) board or would you like me to do you a PCB layout....Would it be quicker for me to build one for you...Daniel.
     
  16. Handjolyna

    Thread Starter New Member

    Jul 25, 2007
    8
    0
    I think whith this extra information I will be able to do it.
    thank again.
     
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