help with FET orientation

Discussion in 'The Projects Forum' started by jakebrown5, Aug 17, 2007.

  1. jakebrown5

    Thread Starter New Member

    Aug 17, 2007
    5
    0
    Hi, this is my first post here. Can anyone help a n00b out with this schematic: http://www.freeinfosociety.com/electronics/schemview.php?id=119?

    I don't know much about electronics and I thought replicating this circuit would be both fun and educating. My question is with the JFETs--Q11, Q12, and Q13-- I've already found that they are 2SK30A-Y but I don't know which are the source and which are the drain legs.

    Also for the BJTs am I correct in saying that the legs with arrows are the emitters?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The key is to get your hands on a manufacturer's datasheet for the device.

    That should have the information you seek along with additional information on the electrical characteristics of the device.

    hgmjr
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Yep, the arrow on the leg marks a BJT's emitter.

    With JFETS, the source and drain are interchangable.
     
  4. jakebrown5

    Thread Starter New Member

    Aug 17, 2007
    5
    0
    I looked through some datasheets for the 2SK30 models and they call them MOSFETs rather than JFETs.......does this mean that S and D aren't interchangable?

    -Thanks
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    The symbols in the schematic are consistent with the representation for JFET as beenthere mentioned.

    Don't know where you are getting the mosfet description.

    hgmjr
     
  6. jakebrown5

    Thread Starter New Member

    Aug 17, 2007
    5
    0
    Here is an interesting link:

    http://www.bdent.com/search/part.jsp?partnum=2SK30A

    The product description states that 2SK30A is a "MOSFET N-Channel" transistor, but the datasheet provided for the 2SK30ATM states that is indeed a JFET. Is this enougher evidence to declare the 2SK30A-Y a JFET with intchangable Source and Drain pins?
     
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I vote that the 2SK30A is a JFET. The evidence cited is the schematic symbol and the fact that schematic appears dated since it uses 1458 Op-amps which date from the mid 80's if not earlier.

    hgmjr
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    In the days of MPF102's, a MOSFET was still a small-signal device with a humongus input resistance. I remember getting then in T)-92 with a piece of spring wire arranged to short the input pins to prevent ESR damage.
     
  9. jakebrown5

    Thread Starter New Member

    Aug 17, 2007
    5
    0
    Yes the schematic is from the late 70's. I have decided to use sockets for those FETs so I can switch their orientation if needed. Thanks for the help. One more thing: Is S3 a momentary switch?
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    No, it's SPDT with a center off position.
     
  11. jakebrown5

    Thread Starter New Member

    Aug 17, 2007
    5
    0
  12. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Nope - that's a flip-flop. No matching needed. they are either in saturation or cut off.
     
Loading...