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MOSFET question

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Pax Writer

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Hello experts

I generally know next to nothing about MOSFETs, and I'd like to study up so I can use one as a switch in an application, but before I jump into it, I have one question:

Is it possible to get a MOSFET which is open when there's no charge on the gate, which will switch fully on/off with only TTL on the gate, and which will conduct upwards of 25A at up to 12V continuously? Or am I dreaming?
I need the MOSFET to turn on a brushed motor on and off with a processor output or similar. Nothing fancy, just stop or full speed ahead.

If my question needs clarification, please just ask, and I'll answer my best.

As for your answers, I don't need much. Yes/no will suffice, a component type suggestion as well would be nice, and in the event that one of you feel like educating me, that will just be a great bonus. Good links are also very welcome.
Thanks.
 
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Most Mosfets need 10V on their gate to fully turn on.
But there are lots of "logic level" Mosfets.

A typical logic level Mosfet is the IRF3711. With only 4.5V on its gate, its max resistance is only 7.3milli-ohms. Its datasheet shows it conducting 100A with only 4V on its gate but only when cold and only for very short pulses because its resistance increases quickly when it heats then it will melt.
The max voltage for an IRF3711 is only 20V.

TTL is a very old logic family that has a high output voltage not much more than only 3V. Logic level Mosfets were designed for newer logic like high-speed Cmos with 5.0V output high voltage.
 
Hi Audioguru
Well, this thing about the TTL was just me not thinking. I mean to turn it on/off from the output of either and 89C2051 or AVR processor, but from your answer, I can see, that I'm better off using some other solution, like for example a relay. Power consumption is as such no big problem, since this circuit will be powered from the same battery which runs the motor (regulated down in voltage, of course).
 
Modern microcontrollers are high-speed Cmos. If their ouput is not driving anything else then their high output voltage is 5.0V which is plenty for feeding a logic level Mosfet.
 
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