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gogo2520

Logic Level Mosfets

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Hello
  I recently started a project, making a step motor controler board using IRLZ44 Mosfets (hex Mosfets) to control the power source to the motors. The way I understand them is they are either on or off no inbetween so if I set the circuit fo 12 volts when the mosfet is trigered 12 volts is sent.
  The board I am working on is using 5 volts for logic and 12 volts for the motor. Someware I read in order for the
      hex-mosfets to work the input voltage has to be twice the output voltage, so that would mean I would have to put 24 volts to the board, the step motors are only rated for 12. So back to were I don't know what I am doing.
  this is the board I am working on  http://pminmo.com/3axis/3axis.htm
  thanks for any help you can offer.
gogo

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You're wrong about how MOSFETs work. They have other modes of operation than just on and off. The gate voltage just needs to be high enough to allow enough current to flow through the load and a small voltage drop across the MOSFET. The maximum gate voltage depends on the device and normally varies between 10V and 20V depending on the device, see the datasheet.

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thanks for the reply Hero999
  I can see were I was wrong with the 24 volts, but it would still need a logic 5 volts to trigger it right. witch is ok because I need 5volts on the board to drive the rest of the logic chips. I guess I need to read some of the Pminmo help forms to see what they were talking about. Something about that particular mosfet. don't know I guess I will just have to  read on.
  Studing the board as it is was worth the learning experience. But as soon as I figure out how the gates and the flip flops work together I plan on doing the driver a different way. The step motors I am using only need 12 volts at max so I could use a uln2803 for the drivers and I want to have opto isolation too.
          thanks again Hero

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