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Whats this Weird Circuit Symbol?

Discussion in 'General Electronics Discussion' started by grom, Feb 18, 2013.

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  1. grom

    grom

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    Dec 5, 2010
    Hi,
    Does anyone know what kind of MOSFET this is? (if it is one... It is some kind of transistor thats for sure.) Its No. is mentioned as RN 4004A ... it seems to be obsolete now and I cant find it anywhere on the internet for replacement. Please help!
     

    Attached Files:

  2. pwdixon

    pwdixon

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    Oct 14, 2012
  3. grom

    grom

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    Dec 5, 2010
    Thanks pwdixon,That really helped :).
    I was wondering If there is a way to find a replacement/newer version of this IC. Can anyone shed light on this?
     
  4. pwdixon

    pwdixon

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    Oct 14, 2012
    Without a datasheet that's a real problem. Though if you had a schematic it might be possible to work out what the part does and work out a replacement that way.
     
  5. Electrobrains

    Electrobrains

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    5
    Jan 2, 2012
    Just seeing the symbol, I think we could guess some things:

    1. The symbol resembles a Symmetrical JFET (in contrast to an Asymmetrical one). Probably the polarity between Source and Drain doesn't matter. The arrows might just be a way to highlight this feature.
    2. The component has the Source marked out. It probably shows the pole where the control voltage of the Gate is referenced.
    3. The full line between Drain and Source could indicate a Depletion type FET, which means it would lead current when Vgs=0V
    4. The Gate line shows a type of MOSFET with isolated Gate: very high input impedance and Voltage Controlling.
     
  6. grom

    grom

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    Dec 5, 2010
    Thanks for the input Electrobrains & pwdixon, please take a look at the circuit where it belongs.
    I'm attaching the circuit diagram with the component ..
    the first is the main part with RN4004. the second one is where the inputs(or outputs?) [A & B] are connected, the third is a diagram of the functioning of the main circuit. Apparently its called a Synchronous detector.
     
  7. grom

    grom

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    Dec 5, 2010
    the ckts
     

    Attached Files:

  8. duke37

    duke37

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    Jan 9, 2011
    These look like a bidirectional insulated gate fet. They operate as switches, one on, the other off in sychronism with the switching input signal.
    I could not find data.
    A 4066 would probably do the same job and maybe replace Q1012 and Q1013 as well.
     
  9. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Hi
    Yes, I too think that the circuit symbol represents something that could be replaced by a bilateral switch.
    But how fast does it have to switch? Maybe the IGFETs outperform the 4066, so what is the frequency of the signal being synchronously detected?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    I think it's possibly a mosfet. It probably originates from prior to the current standard symbology having been decided on.

    But that's just a guess from looking at the circuit diagram.
     
  11. pwdixon

    pwdixon

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    Oct 14, 2012
    I worked on something similar to this in the 80's that was a system that extracted a very low signal from a very noisy input.

    The signal was modulated with the signal input level extracted using a phase sensitive
    detector with the reference signal switching two mosfets.

    In my case the mosfets were switching the signal to ground, in the case of your circuit the mosfets switch the signal directly.

    This means that your device have to be capable of switching a bidirectional signal and probably must not have a drain source diode included, that reduces your choice of parts quite significantly as a great many potential candidates for replacement will include one of these diodes.
     
  12. grom

    grom

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    Dec 5, 2010
    the frequency of the signals is low... max of 160Hz. But the magnitude voltages involved can be anything upto 90V (+/-).
     
  13. grom

    grom

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    Dec 5, 2010
    I went through what a Synchronous detector is and understand the following:

    From diag. 3, Its evident that the weird transistors act as analog switches, able to conduct +/- halves of sine waves with negligible zero crossing error which then add up to give different signals based on phase diff.

    The use is to ultimately extract signal proportional to phase difference between two low amplitude signals(less than noise amplitude a times) and subsequently amplify it to a DC value with an LP filter.

    The inputs are input 1&2 which will be low amplitude AC. the switch is operated by voltages <24 V(possibly <20V) (diag. 2) from the other two transistors.

    This link gave me those surmises:
    http://measure.feld.cvut.cz/system/files/files/cs/vyuka/predmety/A3M38MSZ/SynchrDetectBW.pdf

    Please advise on whether my understanding is right and suggest alternative transistors that might do the same job.

    4066 might be a good choice but i am worried about the maximum Gate voltage that can be applied.
     
  14. grom

    grom

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    Dec 5, 2010
    Pwdixon,
    this circuit performs the same/similar function as you mentioned
     
  15. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Perhaps a switching mosfet with a series diode might do the trick.
     
  16. grom

    grom

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    Dec 5, 2010
    but the diode will require a potential overcome right? and it will allow only unidirectional current. I require barrier free +/- analog conduction when switch is on. Just like a manual wall switch.
     
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