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Re: Best transistors for SEs - other sourcing questions in Australia?

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  • Joseph Charles
    Hi Mr Moo, You can use ordinary BC548 s and BC558 s in your SE s. If you need a little more grunt for your motor, you can sub in a BC337 (NPN). Don t use a
    Message 1 of 3 , Apr 1, 2008
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      Hi Mr Moo,

      You can use ordinary BC548's and BC558's in your SE's.
      If you need a little more grunt for your motor, you
      can sub in a BC337 (NPN).

      Don't use a reversed diode as the trigger. You can use a
      string of normally biased diodes as the trigger if you wish,
      which will give a trigger voltage of around 0.3V - 0.5V
      times the number of diodes. Roughly.

      Or you can use a normally biased standard LED as the trigger.
      A red LED will give a trigger of around 1.7V, I think from
      memory.

      These are nowhere near as efficient as using a
      1381. About the only source in Australia that I know of is
      Robotoz: http://www.robotoz.com.au/
      I haven't used them for awhile, though.

      As regards the motor behaviour: Possibly by turning the motor,
      which is what you mean by 'a prod' I hazard, the motor
      is producing a small voltage across itself that is enough
      to begin to turn on the PNP, which then turns on the NPN,
      which then holds the PNP fully on, and away your SE goes.
      Just a guess...

      Hope that's a help.

      Jo

      --- In beam@yahoogroups.com, "moo_astro_moo" <moo_astro_moo@...> wrote:
      >
      > Hi folks,
      > I'm new to the group and to beam, but I have a question regarding
      > recommendations for transistors to use for FLED or similar SEs.
      >
      > I've picked up a bunch of BC639/BC640 NPN,PNP transistors, but the
      > dern things have the pin ID backwards (i.e. the centre pin is the
      > collector, while the base is pin 1). I find this really irritating,
      > and I always mess it up. I'm wondering what transistors other people
      > use in Aust, and where they get it from. Jaycar is my source so
      > there's a few other options available from them.
      >
      > I have another question too, assuming I connect the SEs correctly, I
      > substitute a reversed diode or two as the trigger component (other
      > than a FLED). Using a 3V solar panel (from dick smith ... sigh), it
      > never seems to trigger, even in bright sun, however if I give the
      > motor (3v, with gearhead) a prod, it happily works away. I'm not sure
      > what the deal is - maybe someone can explain - it needs a higher power
      > to get going, but not much to KEEP it going...
      >
      > Finally, in Australia, what's the best source for solar panels? I get
      > the impression that dicksmith solar panels are inefficient (i.e. low
      > power for their size)...how about the a1381 voltage triggers??
      >
      > thanks
      >
    • Joseph Charles
      The trigger voltages I mentioned in my last post need to have around 0.5V added to them This is the voltage across the PNP s base/emitter junction when the SE
      Message 2 of 3 , Apr 2, 2008
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        The trigger voltages I mentioned in my last post need to
        have around 0.5V added to them

        This is the voltage across the PNP's base/emitter junction
        when the SE triggers.

        So the red LED SE would trigger at around 2V.

        Jo

        --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@...> wrote:

        > You can use a
        > string of normally biased diodes as the trigger if you wish,
        > which will give a trigger voltage of around 0.3V - 0.5V
        > times the number of diodes. Roughly.
        >
        > Or you can use a normally biased standard LED as the trigger.
        > A red LED will give a trigger of around 1.7V, I think from
        > memory.
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