Choosing transistors for a VCA diff pair

Discussion in 'The Projects Forum' started by atferrari, Mar 4, 2008.

  1. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
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    I am in the middle of an impasse in my way to a design with my newborn knowledge on CANbus and decided trying to complete the design of a VCA for a function generator, pending for more than 6 months.

    Accepting that I will reinvent the wheel, my questions:

    a) From this two transistors, which should be the best for using, previously matched?

    2N3904 NPN low signal hFE 40 to 300
    BC337 NPN audio hFE 100 to 360

    Both are really cheap so cost is not a point here.

    b) Given stable / same conditions for the testing of the transistors, should I look for just same Vbe or should I look for same hFE? Measuring Vbe is much easier and faster in a breadboard. Did some practice today.

    I've read a lot in the Web but found too much blah blah on the subject.

    Comments on the whole subject, welcome.

    OTA's are not an option, at least for the moment.
     
  2. John Luciani

    Active Member

    Apr 3, 2007
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    Why not a dual transistor? The transistors are on the same die so there
    temerature will be the same and they should be pretty well matched.

    Checkout the On-Semi website. For example
    NST45011MW6, BC846, MBT3904DW (which is a dual 3904)

    (* jcl *)
     
  3. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
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    Getting them here in Argentina is insanely expensive. That's why my quest of matched discrete.
     
  4. John Luciani

    Active Member

    Apr 3, 2007
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    Is there an On-Semi sales office in Argentina? You could try for some some samples.

    (* jcl *)
     
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