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40703Re: Need suggestions for a motor control chip

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  • dcwjobs2004
    Oct 1, 2009
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      I understand you are using a 5V motor, which means a 5V power supply. Here is a thought for your situation. Use an ordinary 5V CMOS logic chip, such as a 74ACT244 or 74ACT04. You can drive these with 3.3V logic, and they will have the 5V swing you need to drive the logic MOSFETs. You run the drivers off the 5V supply.

      The 74ACT series will give you good transient current drive to the high input capacitance (~1000 pF!) MOSFETs so they will turn on and off quickly. The 74ACT244 is a non-inverting octal driver (drives 8 FETs) in a 20 pin package, and the 74ACT04 is six inverters in a 14 pin package. Pretty much anything in the ACT series will work. The "T" of the ACT means that it takes a TTL level input with threshold of ~1.4V.

      Dave Wyland

      --- In SeattleRobotics@yahoogroups.com, "yellowlaser" <fll-freak@...> 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, FLL-Freak <fll-freak@> wrote:
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      > >
      > > 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!
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      > > 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.
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      > > 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.
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      > > 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).
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      > > 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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