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I'm looking for BJT with low VBE(on) ???

Discussion in 'Datasheets, Manuals and Component Identification' started by Electrobrains, Jan 2, 2012.

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  1. Electrobrains


    Jan 2, 2012
    Now I have searched and measured enough! I think I need some help.

    I am looking for an NPN transistor with a low cut-in voltage/ on-voltage (Emitter-Base voltage that switches on the transistor).
    I know this voltage is physically limited to approximately 600-700mV, but still there are variations between different transistor types.

    I need a cut-in voltage of max. 600mV @ 10mA Ic (room temperature).
    The preferred housing is a TO92 and VCEO>30V

    I could also use some low threshold VGS MOSFET, but I did not find any such type either.

    The old germanium transistors could probably also be used, but there seems not to be any commercial, low-cost types available.

    Thankful for answer!
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Can you tell us the problem you're trying to solve? It may make things easier for us.

    There are circuits where you can have the "turn on" voltage as low as you like.
  3. Electrobrains


    Jan 2, 2012
    I need to switch on a small (20-30mA/12-24V) load with a 0.6V signal.
    The PCB already exist and the circuit is a simple emitter grounded NPN transistor stage.
    There is only space for a small transistor.

    I suppose there must exist some low cut-in transistors among all the existing transistors out there. The problem is, that this spec is usually not searchable in the search machines.

    I have got some wild ideas, like bringing down the cut-in voltage by adding a "heat resistor" in thermal contact with a normal transistor (like BC546B).
    That solution is not elegant though and would also add quite a bit of extra work. Also, such circuit would need heat-up time to function properly.

    I know I could easily use another circuit if I would have the space and could redesign (probably would use a single LM358 - one of my favorite ic's).
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    That particular parameter has more to do with physics than design.

    Try to find an old germanium transistor...

    edit: like this one. (but you're going to run up against problems with Vce(max) for germanium NPN transistors).
    Last edited: Jan 3, 2012
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