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2N2222 transistor to drive a motor ????

Discussion in 'Electronic Basics' started by Ankur, Feb 24, 2004.

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  1. Ankur

    Ankur Guest

    How much current can the 2N2222 transistor bear? Can it drive a motor
    ? I tried doing tht but it got heated up and hFE started changing
    thereby causing the current to increase gradually . The config. i used
    was as follows :-

    ^ ^ Vcc =25V
    ! !
    100k 220ohm
    ! !
    MotoR !
    ! /

    collector current flowing was of the order 100mA ( which increased
    with time due to heating up of transistor )
    Vcc might seem a lil high but below tht , the motor cudn't drive .

    Basically , i need to drive a motor from a digital +5V ... the above
    circuit was just 2 test the current capacity .
    I also wanna know whether an AND gate output can drive this ? It was
    switching the transistor perfect but collector current was too small .
  2. CBarn24050

    CBarn24050 Guest

    your 100k resistor is too high, try 4k7 instead.
  3. Tim Dicus

    Tim Dicus Guest

    The current capacity should be ok if you connect the motor correctly. Replace the 220 ohm resistor with the motor and the 100K
    resistor with a 4.7K.

    Hope that helps.

  4. Tim Dicus

    Tim Dicus Guest

    You also might want to put a diode (like 1N4001) in parallel with the transistor, anode to the emitter and cathode to collector.
    That will prevent flyback voltage from damaging the transistor when the current flow is cut off by the transistor. This applies also
    to relays or any inductive device.

  5. ****************************************************************************

    All Bipolar transistors change gain with heat!

    There are sacrificial methods of stabilizing the transistors gain.

    BUT! You are misssing the point!

    Your circuit only wants to be a SATURATED driver. (On-Off Switch)
    So drive the base with the MOST current necessary to maintain saturation in
    the worst case.
    You have not said what generation your AND gate is, so I have no idea if it
    can drive the base
    correctly in current.

    | __O Thomas C. Sefranek
    |_-\<,_ Amateur Radio Operator: WA1RHP
    (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz
  6. Tim Dicus

    Tim Dicus Guest

    Change that to read...

    Put the diode in reverse polarity across the motor.

    My bad. I violated my own prime directive. "Start brain before engaging mouth..."

  7. CFoley1064

    CFoley1064 Guest

    Subject: Re: 2N2222 transistor to drive a motor ????
    Tom is right -- you're getting heating on your 2N2222 because it's not
    saturating. A saturated NPN transistor will have a Vce (voltage between
    collector and emitter) of around 0.3V or less. Power across the transistor is
    calculated as Vce * I. If you've got 2 or 3V across your transistor, and
    you're driving a 100 mA load, your power dissipation will be high (200 to 300

    Digital logic gates have specified maximums as far as how much current they can
    drive, and you didn't specify which logic gate you're using to drive the
    transistor. As a result, can't give you more than general advice about how to
    do this.

    If you've got a TIP120 (available at Radio Shack), you might want to try this
    circuit -- it will work for any logic gate operating at 5VDC (view in fixed
    font or M$ Notepad):

    Logic Motor Driver
    | |
    .---o----. |
    | + | |
    | | |
    | | |
    Motor (100 mA)| - 1N4002
    | | ^
    | | |
    | - | |
    '---o----' |
    | |
    10K |
    ___ |/ TIP120
    o----|___|-o-----| NPN DARLINGTON
    Logic Input | |>
    .-. |
    10K | | |
    | | |
    '-' |
    | |
    === ===

    A saturated darlington will have a little more than 1V from collector to
    emitter. You'll then have 1V * .1A = .1W across the darlington, so you won't
    need a heat sink.

    Good luck
  8. CFoley1064

    CFoley1064 Guest

    By the way, you might want to try downloading a freeware copy of

    Andy´s ASCII-Circuit v1.24.140803 Beta

    available at

    It's very helpful for batting out snippets of circuits for text only

    Good luck
  9. Jamie

    Jamie Guest

    it looks like your not saturading the transistor enough.
    this can lead to heating because the junctions are not at
    their lowest resistance point.
    if over speed is an issue then place a dropping resistor at the
    emitter to componsate for the over speed. this way you can keep the
    transistor at saturation but it may cause poor regulation if load
    varies on the motor.

    if you don't need variable speed then use a HexFet transistor they
    can switch on at very low resistance thus causing far less heating.
  10. David Wood

    David Wood Guest

    "2N2222 datasheet" in google nets multiple links to sources for the data.
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