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40709Re: [SeattleRobotics] Re: Need suggestions for a motor control chip

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  • Tony Mactutis
    Oct 1, 2009
      Skye, Fairchild makes lots of mosfets that will work at 3.3v. Here are
      a couple:

      NDS8434 (p-channel)
      FDN337N (n-channel)

      To find them, go on digikey and search for 'logic level mosfet'. Then
      look in the 'Rds On' column for ones that have their on-resistance
      specified at 4.5V. They are not going to work as well at 3.3V as they
      will at 5V, but they are usable, if you keep their power dissipation
      within limits.

      Note that for p-fets, you may need to add an n-fet with a pullup to
      control them, because otherwise you won't be able to get their gate up
      to the positive rail to turn them off.

      Tony

      yellowlaser wrote:
      >
      >
      > Update:
      >
      > I managed to get something working last night. Turns out I had three
      > cascading problems that prevented the transistor/FET method from working.
      >
      > I controlled a 2n2222 transistor from the micro. The 2n2222 switched
      > the raw system voltage (~9 volts) used to control the gate of the FET.
      > This was enough voltage to turn on the FET. Works well at 20KHz.
      >
      > I still do not like the solution due to the extra parts and would
      > still love a suggestion for a good part.
      >
      > -Skye Sweeney
      >
      > --- In SeattleRobotics@yahoogroups.com
      > <mailto:SeattleRobotics%40yahoogroups.com>, FLL-Freak <fll-freak@...>
      > wrote:
      > >
      > >
      > >
      > > I am interested in controlling a 5 volt 1 amp  DC brushed motor
      > using 3.3V logic. I would like speed control via PWM but do not need
      > to reverse direction. I am thinking a full h-bridge is an overkill. A
      > simple FET/switch/ 'thing' must exist to do this!
      > >
      > >
      > >
      > > I have been playing with varius MOSFETS and found that they need
      > more than the 3.3 volts I have from the micro to turn them on. I have
      > a tube of IRLD024 logic level FETS, but they are 5 volt logic not 3.3.
      > I can't seem to find a similar part for 3.3 volt logic.
      > >
      > >
      > >
      > > I tried using an NPN transister to switch a higher control voltage
      > to the FET, but for whatever reason that does not seem to work. It
      > also increases the part count considerably.
      > >
      > >
      > >
      > > I have tried some Avago solid state relays such as the ASSR-1511 but
      > found the switching speed is very limited (about 2K Hz). I would at
      > least like to modulate the motor outside of hearing range (> 18KHz).
      > >
      > >
      > >
      > > I have done a fair amount of poking around, but can't find the right
      > key words to find a suitable part. Any suggestions would be most welcome.
      > >
      > >
      > > -Skye Sweeney
      > >
      >
      >
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