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Circuits with semiconductor devices

Discussion in 'Mathematics and Physics' started by PG1995, Oct 15, 2013.

  1. PG1995

    PG1995 Active Member

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    Hi

    Could you please help me with this query about Shockley diode? Thank you.

    Regards
    PG

    PS: For etymology of the words "thyristor" and "thyratron", please have a look on this PDF.
     

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    Last edited: Oct 16, 2013
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi PG,
    The current flowing thru the resistor and diode [ when the cap has discharged] is less than the required HOLDING current of the diode, so it turns off.
    Look at this pdf.
    E
     

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  3. PG1995

    PG1995 Active Member

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    Thank you, Eric.

    The following definition from the PDF is very helpful.

    Regards
    PG
     
  4. dave

    Dave New Member

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  5. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    ONLINE

    You will also find a minimum holding current specification for SCR's (Thyristors): http://www.onsemi.com/pub_link/Collateral/HBD855-D.PDFIt is listed as IsubscriptH.

    John
     
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  6. PG1995

    PG1995 Active Member

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    Hi

    Could you please help me with these queries about a UJT (unijunction transistor)? Thank you.

    Regards
    PG
     

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  7. killivolt

    killivolt Well-Known Member

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    I can't event read that .jpg

    Never mind, it's my new viewer, I have to click on the Web version.

    Edit: Thanks for the post, I never even new there was a UJT. Until now.
     
    Last edited: Oct 15, 2013
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  8. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi PG,
    This pdf explains the valley voltage characteristic of a UJT
    Dont forget the UJT is formed using a 'semiconductor' material, so it will have an intrinsic resistance from B1 to B2, usually around 10K
    E
     

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  9. PG1995

    PG1995 Active Member

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    Thanks, Eric.

    I understand this but it's an n-type material which means it has some free electrons which means a bad conductor, and a bad conductor isn't really such a good insulator that it can offer resistance of 10 kΩ. I know I'm missing something here. So, I still need a little more help with Q1 here, and if possible, please do let me know if my interpretation in Q2 is okay.

    Regards
    PG
     

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    Last edited: Oct 17, 2013
  10. PG1995

    PG1995 Active Member

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    Hi

    Could you please help me with this query about a UJT? Thanks.

    Regards
    PG
     

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  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi PG,
    I would agree with you, the statement appears ambiguous, look at this links equations for comparison.
    http://www.circuitstoday.com/ujt-relaxation-oscillator

    In practice using UJT's I have found that if R1 value is too low, the UJT will turn ON as expected, but will never turn OFF.
    Eric
     
  12. PG1995

    PG1995 Active Member

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    Hi

    Could you please help me with these queries? This text will provide you with full context. Thank you.

    Regards
    PG
     

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  13. JimB

    JimB Super Moderator Most Helpful Member

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    Q1
    Wire 5 and wire 6 have a physical presence so there will be capacitance between them.
    If the electrical connections to the right hand side of wires 5 and 6 have exactly the same characteristics, then the voltage across C_n will be zero, and that capacitance will have no effect on operation.
    If wires 5 and 6 have different electrical loads at their right hand sides, then as the voltage from wire 2 varies, then the voltages on wires 5 and 6 will be different, and so C_n becomes significant.

    Q2
    The double capacitor with the centre tap connected to ground is just an easy way of drawing two separate capacitors,
    (one capacitor from wire 5 to ground, the other from wire 6 to ground), in a limited space on the screen/paper.

    JimB
     
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  14. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi,

    Just a quick note here...

    I see a lot of questions about the unijunction transistor. These transistors are rarely used these days. I have only encountered one real circuit that had one in it in the last 40 years. There may still be schematics around though and there's a chance someone somewhere might use one, but i think it will be very rare.
     
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