Transistor that has TWO emitters & Servo amp

Discussion in 'General Electronics Chat' started by DexterMccoy, Mar 1, 2014.

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  1. DexterMccoy

    DexterMccoy Thread Starter New Member

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    What is this type of transistor called, and what kind of circuit's is it used in and for?

    The Transistors have a X crossing in the Servo amplifier, what does this X crossing do?
     
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  2. DexterMccoy

    DexterMccoy Thread Starter New Member

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    here are the schematics for them
     

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  3. DexterMccoy

    DexterMccoy Thread Starter New Member

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    This transistor has Two Emitters, look at the schematic

    What is it called and what kind of circuits is it used for and why does it have 2 emitters?
     
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  4. DexterMccoy

    DexterMccoy Thread Starter New Member

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    Servo Amp Q25 goes to Q29
    and Q26 goes to Q28

    What does this do? it's an X crossing pattern
     
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  5. shteii01

    shteii01 Senior Member

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    That is not X crossing. There is no big black dot in the middle of the X.

    What you have is two wires that run from emitter of one transistor to the base of another transistor. The two wires are not connected to each other.
     
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  6. DexterMccoy

    DexterMccoy Thread Starter New Member

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    It seems they are used for RF modulation or modulation circuits for somereason but why 2 emitters?
     
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  7. shteii01

    shteii01 Senior Member

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    One goes to transformer, another goes elsewhere.
     
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  8. DexterMccoy

    DexterMccoy Thread Starter New Member

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    But why use the 2 emitters to do this? for what reason?
     
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  9. Papabravo

    Papabravo AAC Fanatic!

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    They are the basis of TTL circuits and perform an AND function.
     
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  10. DexterMccoy

    DexterMccoy Thread Starter New Member

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    But why the 2 emitters? what does having 2 emitters do? why not 2 bases? or 2 collectors?
     
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  11. Papabravo

    Papabravo AAC Fanatic!

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    Well an emitter will source current. So in a logic gate, if both emitters are high, there is no current flow from collector to either emitter and the transistor is off. This allows the collector to be pulled high.

    In logic terms "A high AND a high is a high"

    If either of the emitters is pulled low then the transistor is on and the collector is pulled low as well.
     
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  12. DexterMccoy

    DexterMccoy Thread Starter New Member

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    does a Base sink or source current?
    Does a collector sink or source current?
     
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  13. Papabravo

    Papabravo AAC Fanatic!

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    In an NPN the base and collector will both sink current and th emitter will source current. For PNP it is the reverse.
     
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  14. DexterMccoy

    DexterMccoy Thread Starter New Member

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    So why do they want to "choose" the pins that source current than to sink current?

    They aren't using the multiple emitter transistor as an ampilifer

    They are using the multiple emitter transistor as a Switch? so choosing sourcing current or sinking current shouldn't be a problem right? they could hook the signals to any pins of the transistor because it's used as a switch
     
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  15. DexterMccoy

    DexterMccoy Thread Starter New Member

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    SERVO AMP PICTURE:

    servo Amp Q25 goes to Q29
    and Q26 goes to Q28

    What does this do? it's an X crossing pattern
     
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  16. shteii01

    shteii01 Senior Member

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    The two wires don't actually connect in the middle, so the current from one wire DOES NOT enter the other wire.
     
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  17. DexterMccoy

    DexterMccoy Thread Starter New Member

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    Yes I know that, I'm not asking about that

    The X crossing pattern is a push pull arrangement?

    Because Q25 goes to Q29 WHY?
    Why does Q26 goes to Q28?

    Is this some type of push pull arrangement or what?
     
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  18. ifixit

    ifixit Well-Known Member

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    The circuit is an H bridge motor driver. The two sides of the "H" must work in an opposite manner with respect to each other... hence the crossover connection.
     
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  19. Billy Mayo

    Billy Mayo New Member

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    Why do servo motors need an H bridge driver? What does the crossover connection do? If no crossover connection what will happen?
     
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  20. Papabravo

    Papabravo AAC Fanatic!

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    The purpose of an H bridge is to steer the current through the motor coil in both directions. In one of the directions the motor moves in the clockwise direction, and in the other direction it moves counter clockwise. A uni-directional servo motor is only useful for producing a controlled velocity. For position control it is like a WOM (Write Only Memory)
     
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