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Zener Diode in Circuit Diagram

Discussion in 'General Electronics Chat' started by bigal_scorpio, Dec 15, 2007.

  1. bigal_scorpio

    bigal_scorpio Active Member

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    Hi to all,

    Just wondered if anyone can tell me the reason that the Zener diode in the table below Fig.1 has the same value resistor for all the values of Zener's?

    It seems to me that they have gone to the trouble of making a table for no good reason or is there an error somewhere, I mean whats the point of making an if then scenario when all the thens are the same? :confused:

    Thanks for looking..........Al
     

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  2. Styx

    Styx Active Member

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    its being used as a crude voltage regulator. The supply coming in is 12V, but this chips takes a Vcc of 5V max
     
  3. bigal_scorpio

    bigal_scorpio Active Member

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    Zener query


    Yeah, I get the voltage reg part, but why the table with the different Zener's and the same resistor values?

    Is there a reason? :confused:

    Al
     
  4. dave

    Dave New Member

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  5. Styx

    Styx Active Member

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    ahh I see what you mean. Yer seems odd. Its like "whatever rail you are gonna run from, use a 82k resistor"

    would of been easier just to say that
    UNLESS typo in the datasheet
     
  6. kchriste

    kchriste New Member Forum Supporter

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    I guess it isn't any more silly than R2 in that circuit. :D
     
  7. Roff

    Roff Well-Known Member

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    R2 will discharge C1 all the way to ground (I know, it will never fully discharge) when the 12V supply is turned off. Without it, the last volt or so might take a while. Why that would matter is another question.
     
  8. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Al,
    Unless I am having a 'senior moment' the R4 resistor isnt connected to the Zener???

    It refers to the R/C timing for the Tone Gen ic.

    R1 is the zener drive resistor.
     
  9. eblc1388

    eblc1388 Active Member

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    I must be having a senior moment because the datasheet stated that the IC has max. operating current of 800mA.

    A 1K+zener arrangement to provide 800mA to the IC?
     
  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,

    The operating current stated is for the full circuit Fig1 NOT the zener.

    The R1/Z1 supplies the Tone Gen NOT the whole circuit....:p
     
    Last edited: Jul 7, 2008
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The IC is Cmos so it draws hardly any current.
     
  12. eblc1388

    eblc1388 Active Member

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    I have to re-read the datasheet once again just to be sure.

    I bet to differ. It is clearly stated that at VCC=5V and in an arrangement as Fig.1 the operating current of the IC is 800mA max.

    Obviously the datasheet is wrong.
     
  13. Roff

    Roff Well-Known Member

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    I would bet good money that's a typo, and it is supposed to be 800uA. 4 watts dissipation in an 8 pin dip? More like a 6-color smoke generator than a 6-tone sound generator.
    As you said, the datasheet is wrong.
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The IC is a low current Cmos one. Its output current is only 5mA and the dalington transistors amplify it to a peak current of 10V/8 ohms= 1.25A. The duty-cycle reduces the entire circuit's average current to 800mA.
     
  15. Roff

    Roff Well-Known Member

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    You're probably right. The current spec does say "(Referrence [sic] Fig.1)". Fig.1 is the entire schematic.
     
  16. Gordz

    Gordz New Member

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    I would think that the value of the zener depends on the supply voltage. The chip is rated from 2 to 5 volts and the zener is part of a crude regulator, the lower values would be for lower supply voltages to lessen the effect of supply on frequency. Bit of a naff setup...
     
  17. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    morning Ron,
    Thats the way I read it also, the 'circuit' current not the ic alone.

    hi Gordz,
    The R4 table relates to the ic oscillator, not the zener diode feed resistor.
    The circuit shows a +12Vsupply., R1 and a Zener.

    I think we all agree parts of the spec description are a little 'naff'.;)
     

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