Simple question, logic level transistors from technobots online

Discussion in 'General Electronics Chat' started by hspalm, Aug 11, 2010.

  1. hspalm

    Thread Starter Active Member

    Feb 17, 2010
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    8
    Hi
    I found something called "logic level transistors" under mosfets on technobotsonline.com. Does this mean they are primarily used in switching? Am I wrong when saying this is perfect for pwm controlling a dc motor with a microcontroller or similar logic output?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    More accurately, they're called "Logic level MOSFETs".

    Very generally, such MOSFETs are considered fully ON when Vgs>=4.5v, where Vgs is the voltage on the gate using the source terminal as the reference.

    You might use a uC to directly drive the gate of such a MOSFET for simple ON/OFF type control, or very low-frequency PWM. However, keep in mind that the drive capability of most uC's is limited to around 20mA, so that means you'll need to use a ~220 Ohm resistor between the uC's I/O pin and the gate of the MOSFET.

    2N7000 N-ch MOSFETs come in a TO-92 package, and for practical purposes can sink up to 100mA.
    A nifty MOSFET is the IRLD024; it comes in a 4-pin DIP package which makes it great for use with breadboards and protoboards. These are rated for up to 60v and 2.4A drain current, but a practical limit is 1.2A or less.
     
  3. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Thank you very much for your fullfilling answer!
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    We've come a long way from the first transistors I ever had, I somehow doubt anyone here is old enough to remember the 2N107, 2N170 and CK722. Those were your only choices as an experimenter in the early days and while I built a few circuits with them that actually worked the whole principle of current amplification was a mystery to me so I stuck with my trusty old vacuum tubes for years afterwards.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Yours had industry numbers? The first ones I saw were in metal tubes about the size of a 3/8" length of ballpoint refill tube. The leads were red, yellow, and blue - about 36 ga wire. They mounted in bitty nylon clips. Seymour Cray used them in the first Univac computers.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    First I recall that were actually offered to the public as an experimenter's transistor. These allowed you to drive an actual speaker off your crystal radio set. :)
     
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