switching using a 2n700

Discussion in 'General Electronics Chat' started by jonisonvespa, Jan 2, 2013.

  1. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    hi
    im building an auduino project, im trying to switch 2 * +5v into two pins not having much luck in my circuit, this is the circuit im using seems to do the opposite when the switch is made ive got a 0v to pin could someone please check my circuit thanks
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    Maybe I'm just tired, but I don't know what you are trying to do....

    Your circuit will only have 5V on the output when the input to the 2N7000 is below the threshold voltage(logic 0) as the transistor will not be conducting. The 1kΩ resistor pulls the voltage up to +5V.

    When the input to the MOSFET is above the threshold voltage, the transistor will conduct, pulling the output to 0V.

    Why not simply use the switch? Why is the MOSFET there at all?
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Why would you expect it to be otherwise? When you apply 5V to the gate the transistors turns on and pulls the pin low.
     
  4. jonisonvespa

    Thread Starter Member

    Mar 25, 2012
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    i thought it would be interesting to try another way to switch a +5v instead of a button
    ok i understand now, why im getting a gnd when +5 is present at the gate

    how else could i get a +v to my pin instead of using a push button / switch?

    thanks
     
  5. tshuck

    Well-Known Member

    Oct 18, 2012
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    A wire.







    Any other method is really just using a variation of what you would be doing with a switch. A transistor, a relay, a transmission gate, etc. will all require you to switch an input, which will probably be... a switch...
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    The single Mosfet is an inverter. Add another transistor or Mosfet to make it invert twice then when the input from the auduino is high then the output is also high (but with fairly low current provided by the 1k output resistor) and when the input is low then the output will also be low.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    You are not using a Vgs TTL level MOSFET, so the output may not as your expected.
    You may try to use a transistor to be your switch:
    http://www.electronics-tutorials.ws/transistor/tran_4.html

    Or you can search on google :
    1. Using a transistor as a switch.
    2. Using a MOSFET as a switch.

    You can learn more about how to using a transistor or MOSFET to be a switch.
     
  8. tshuck

    Well-Known Member

    Oct 18, 2012
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    A MOSFET is a transistor, I think you mean BJT....
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    Yes.
    Although the BJT and MOSFET are all belongs to Transistor, but BJT is the abbreviation of Bipolar Junction Transistor, normally when we say transistor that is talking about BJT, and say MOSFET is talking about MOSFET.

    If you type 'transistor' to search on google then you will know what I mean.
     
    Last edited: Jan 2, 2013
  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    And MOSFET stands for Metal–Oxide–Semiconductor Field-Effect Transistor..
    What google has to say about this is irrelevant, this is a site dedicated to electronics in detail, so when you make a distinction about types of transistor I think you should say "bjt or mosfet", not "transistor or mosfet".
     
    tshuck likes this.
  11. Audioguru

    New Member

    Dec 20, 2007
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    With a 5V supply and a 1k output resistor then the max output current is only 5mA. the 2N7000 Mosfet is spec'd to conduct very well when its gate-source voltage is only 4.5V so it will work fine.

    But why is the output resistor chosen with such a high value (1k) that the max output current is nearly nothing? The arduino can supply much more current WITHOUT the Mosfets.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    The first transistor is the BJT, so the transistor is represent the BJT as the Ancestor of transistors, use BJT that just emphasize the transistor which talking to is a BJT, sometimes I also do that.

    Although there are many kinds of transistors developed, but when I say transistor that is point to a BJT, when I say some other transistors then I will type the name of that kind of transistor as MOSFET or JFET or UJT.
    Although we discussing on this site, but If you want to get some more infos then you can't just search on this site, that is not enough, so when you search the EE infos on google, if you use bjt to search will get less info than transistor.

    Here is some search compared form google.
    using bjt as switch - About 405,000 results (0.35 seconds)
    using transistor as switch - About 14,300,000 results (0.17 seconds)
    bjt - About 10,900,000 results (0.17 seconds)
    transistor - About 63,800,000 results (0.20 seconds)

    Don't tell me that you don't want to search on google.

    So when I say transistor and MOSFET, I don't think there is nothing wrong, it's very clear that is pointed two different parts, I think there are many people will doing the same thing as I did.
     
  13. tshuck

    Well-Known Member

    Oct 18, 2012
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    Actually, FETs were the first transistors. They were patented and described in depth well before a BJT was ever created. The BJT was the first one created, but was only by accident while waiting for the technology to create a FET.

    It doesn't matter what misrepresented data there is on the internet a transistor is not a BJT. A BJT is a transistor.

    This would be like saying I you need to pick between a fruit and an orange.

    I'm glad we can all agree!:D
     
    kubeek likes this.
  14. ScottWang

    Moderator

    Aug 23, 2012
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    Thanks.
    I thnk many people will treat the BJT as the first transistor like me.
    This is the missing part of the transistor developing history to me.
    Can you get some more infos about this?
     
    Last edited: Jan 2, 2013
  15. tshuck

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    Oct 18, 2012
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  16. ScottWang

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    Aug 23, 2012
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  17. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    What? All four are in english. Maybe try setting the language in the top right corner on the first two links?
     
  18. ScottWang

    Moderator

    Aug 23, 2012
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  19. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Those are french and belgian applies for the same patent, see the "Also published as:" line right next to it?
    Click on "original document" in the menu on the left.
    If you cant navigate a web page, do you think you will understand the language of patents? ;) I rarely have the guts to read them all the way through.
     
    Last edited: Jan 2, 2013
  20. ScottWang

    Moderator

    Aug 23, 2012
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    Thanks.
    I get into the web pages as you mentioned, and choosing the Original document to see, there are so many english documents , the last times that I get into the same page, but I didn't choose the original documents.

    I want to know about what tshuck mentioned that FET is the first transtistor, I would like to know the history like a story.
     
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