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bjt in parallel operation

Discussion in 'Electronic Basics' started by nanotech1, Apr 3, 2005.

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  1. nanotech1

    nanotech1 Guest

    can someone help me

    i need info on how to operate bipolar transistor in parallel
    for higher current output

    is there any rule of thumbs
    on the designing sutch circuit without blowing the bgt's all together

    i want to build my own high power rf generator for induction heating

    any help appreciated
     
  2. I'm not sure if this is the rule-of-thumb you are looking for,
    but you need to either degenerate with emitter resistors
    (simple) or control relative base currents (harder) so as
    to avoid having one transistor conduct most of the current
    due to its Vbe getting lower because it is hotter because
    it is conducting more current. (You want to get the gain
    of that partially thermal feedback loop enough below 1
    that the parts share current about equally.)
    The current hogging problem is almost nonexistent with
    MOSFETs because of their positive TC of channel R.
    For similar reasons, they are far less prone to second
    breakdown effects too. I would look into using them.
     
  3. Active8

    Active8 Guest

    " || "
    Something I've *always seen* in || bjt apps.
    Show me an example of one working circuit using this approach.
    At least you hinted that *Vbe required to maintain constant I_C*
    drops with temperature instead of talking about DC beta increasing,
    but that thermal feedback loop thing may be just a bit much for the
    OP. We're in seb now.

    But the OP can google on Ebers-Moll and Gummel-Poon for a
    not-too-sadistic explaination of V_BE/V_T and all that.
    Except in the sub-threshold region.
    I would google on induction heater mosfet and induction heater IGBT.

    IGBT applications induction heater

    MOSFET applications induction heater

    IGBTs seem to be cropping up in those things lately.

    http://www.fairchildsemi.com/products/discrete/ind_heating.html

    http://www.dansworkshop.com/Induction Heating.shtml
     
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