NPN type transistor

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Discussion in 'General Electronics Chat' started by aGpLT, May 26, 2010.

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  1. May 26, 2010 #1
    aGpLT

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  2. May 26, 2010 #2
    BMorse

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    2n3904's should do, they are just switching a relay load... and I would change the base resistor to something smaller like a 330 or 470 ohms.....

    B. Morse
     
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  3. May 26, 2010 #3
    SgtWookie

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    If you are driving the transistor's base from a PIC, don't go below 220 Ohms or you will fry your PIC's output port.

    Better to stay between 330 and 470.
     
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  4. May 26, 2010 #4
    Norfindel

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    What current does the relay coil require?
     
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  5. May 26, 2010 #5
    aGpLT

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  6. May 26, 2010 #6
    Wendy

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    I suspect the reason it didn't work is base current. As a general rule of thumb base current is 1/10 of collector current for reliable switching. With a 10KΩ base resistor and (I assume since it wasn't specified) and 12VDC you have 1ma on the base. If the power is 5VDC it is under 0.5ma.

    You really need to know the collector (relay coil) current.
     
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  7. May 26, 2010 #7
    studiot

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    You need to drive the transistor into saturation for this circuit to work. That is why 1ok base resistor is too high.
    Alternatively a switching FET would do the job.
     
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  8. May 27, 2010 #8
    aGpLT

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    Jan 21, 2010
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    Heh its quite weird... i used two 2n2222a on one hbridge of 3 and its working fine, but when i trying other two (identical) it dont show any life. nope i am lying everything is not working.
     
    Last edited: May 27, 2010
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  9. May 27, 2010 #9
    wannaBinventor

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    Have you tried switching the resistors yet? I would think 2n2222s would be just fine so long as they received ample base current.
     
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  10. May 27, 2010 #10
    aGpLT

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    yeah now i am using 470R resistors. base controlling with pic16f88. uC output current 20mA, required for base current 15mA when collector current is 150mA, relay coil current 40mA. I think everything should be ok, but...
     
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  11. May 27, 2010 #11
    wannaBinventor

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    Make sure that your transistor pins are oriented correctly. When I first started in electronics (oh..... 8 weeks ago), I kept forgetting that the pinout I was looking at showed it with the pins facing UP - hence I had the collector and the emitter reveresed. Make sure that you haven't done that.
     
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  12. May 27, 2010 #12
    aGpLT

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    I know pin out quite well, http://www.buxcomm.com/catalog/images/mp2222_small.gif easy to remember.
     
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  13. May 27, 2010 #13
    radiohead

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    If the General Purpose 2N2222 or 2n23904s get too hot, try a D40D8 or a TIP-41-series NPN transistor with a heat sink. Of course, the base will need a small current to allow it to "turn on."
     
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  14. May 27, 2010 #14
    bertus

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    Hello,

    I did have a look at the RM84 datasheet.
    It says at the coil data block that the rated power consumption is 0.4.. 0.48 Watt.
    This implies a current of 80 to 96 mA @ 5 Volts.

    Bertus
     
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  15. May 27, 2010 #15
    aGpLT

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    Jan 21, 2010
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    its more than enough for 2n2222a because at 150mA it requires only 15mA to open. everything should work :/
     
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  16. May 27, 2010 #16
    bertus

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    Hello,

    A 2n2222A is a little bit lean for it.
    The 2N2219 can handle a bit more.
    See the attached datasheet for the 2N2222 + 2N2219
    I also attached a transistor table for you (unzip it to read in excel or open office).

    Bertus
     
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    Redstone2 and aGpLT like this.
  17. May 27, 2010 #17
    aGpLT

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    Jan 21, 2010
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    Thank You, i will post tomorrow about my progression.
     
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