Transistor Question

Discussion in 'General Electronics Chat' started by TomWhitfield, Apr 5, 2013.

  1. TomWhitfield

    Thread Starter New Member

    Apr 5, 2013
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    Hi all,

    I've registered to this forum simply to ask a question regarding my transistor :)

    I have a circuit which is powered by 12v, my transistor is getting really hot (cannot touch it for long before it burns my fingers!). My circuit works fine for a short amount of time, then it just stops functioning. if I turn off the power for a few hours and come back, it's working again.

    Does this sound like a heat problem? Would the heat prevent the transistor from functioning? I am new to electronics but the project I'm doing is almost done, it's just annoying that it only works for 5-10 minutes before deciding to give up.

    All details are below for the type of transistor I'm using...


    TRANSISTOR, NPN, TO-92
    Transistor Polarity:NPN
    Collector Emitter Voltage V(br)ceo:40V
    Power Dissipation Pd:625mW
    DC Collector Current:600mA
    DC Current Gain hFE:300
    Transistor Case Style:TO-92
    No. of Pins:3
    Collector Emitter Voltage Vces:200mV
    Continuous Collector Current Ic Max:600mA
    Current Ic Fall Time Measurement:10mA
    Device Marking:2N2222
    Fall Time @ Ic:250ns
    Full Power Rating Temperature:25°C
    Gain Bandwidth ft Min:300MHz
    Gain Bandwidth ft Typ:300MHz
    Hfe Min:75
    No. of Transistors:1
    Package / Case:TO-92
    Power Dissipation Pd:625mW
    Termination Type:Through Hole



    Thanks in advance people! :)
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    If you post a schematic over here, we can have a look if these is something wrong with it.

    Bertus
     
  3. TomWhitfield

    Thread Starter New Member

    Apr 5, 2013
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    0
  4. bertus

    Administrator

    Apr 5, 2008
    15,645
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    Hello,

    What are the ratings of the motor?
    What is the value of the resistor in the base of the transistor?

    Bertus
     
  5. TomWhitfield

    Thread Starter New Member

    Apr 5, 2013
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    0
    Resistor Info

    470 Ohm 0.25W Resistors
    CR25 high stability carbon film Resistors
    Operating Temperature: -55 to +125 C
    Wattage: 0.25W
    Max. working voltage: 300V
    Max. overload voltage: 600v
    Body dims. (L x dia): 6.5 x 2.5mm
    Leads dims. (L x dia): 28 x 0.6mm

    I'm not 100% sure on the motor I'm afraid, all I know is that it is a 12v motor, 300RPM & uses around 5W @12v DC.

    Hope this helps?
     
  6. WBahn

    Moderator

    Mar 31, 2012
    17,715
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    If the motor is using 5W at 12V, then that says that the motor current can be on the order of 500mA. That's pushing the max ratings of that poor 2N2222 pretty hard.

    You are giving out tons of detailed spec information but not very much of the basic information that is really needed. For instance, what is the voltage that is being put on the "GPIO Pin 18" when you are turning the motor on?

    Let's say that it is 5V. That means that you have about 4.3V across the 470Ω base resistor. Let's call it 4.7V so that we are getting about 10mA of current into it. I don't know how far into saturation you are going to get with that base current. Can you measure the voltage across the collector and emitter pins while the motor is running?
     
  7. TomWhitfield

    Thread Starter New Member

    Apr 5, 2013
    5
    0
    Hi WBahn, thanks for the response.

    I do not own a voltmeter unfortunately. I was following a build log and I noticed the guy was using 6v for power and not 12v, I just chose the transistors he recommended. As I said, it works perfectly but decides to stop randomly (I just presumed it was due to the heat).

    Could you possibly provide me with a model of transistor that should be able to cope a lot better than the current one? Ideally using the below site so I could pick some up from the store tomorrow :)

    http://www.maplin.co.uk/productsearch?criteria=transistor

    Thanks! :)
     
  8. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    You need a bigger transistor with a heatsink.
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,715
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    The site just wanted to keep loading cookies on my machine. My tolerance for that is very low.

    I did see that they had mutlimeters for as low as 8 (pounds?). Get one.

    You can probably get by with most any general purpose transistor that is in a TO-220 or similar case. I saw they had TIP3055s. That's probably overkill, but would work (provided you can get enough base current into it).

    We still need to know what you are using for your input. How many volts and what kind of current is it capable of?
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What is the voltage of your GPIO input?
     
  11. timescope

    Member

    Dec 14, 2011
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    What of a logic level mosfet ?

    Bipolar transistors need huge base currents to get them to saturate properly at high current levels.

    The 2N2222 datasheet specifies Vce sat = 1.0 v @ Ic = 500mA, Ib = 50mA.

    Timescope
     
  12. TomWhitfield

    Thread Starter New Member

    Apr 5, 2013
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    The GPIO pin is giving out 3.3v I believe. (It's a raspberry Pi).
     
  13. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I would use a logic level MOSFET. Second choice would be a Darlington.
     
  14. WBahn

    Moderator

    Mar 31, 2012
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    Then you are probably going to have a hard time getting enough base current into a single transistor. You can use a Darlington or a MOSFET.
     
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