Need help with function generator output

Discussion in 'The Projects Forum' started by runningrage, Apr 15, 2010.

  1. runningrage

    Thread Starter New Member

    Apr 14, 2010
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    I having problem getting NPN transistor to turn-on with
    GF-8046 function generator i don't know why i can't get the transistor to turn on. I check the voltage and current output im getting voltage reading but no current at all. Do you have to use something before the transistor base to turn it on. If anyone can help here with advice on how to turn on transistor with funciton generator
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    "Do you have to use something before the transistor base to turn it on. "

    Yes, a base resistor, to limit the current through the B-E junction. Since you are now getting no current, you probably blew the junction open. Do an Ohmmeter check between the base and emitter. If it's OK, you will get a reading with + to base and - to emitter.

    Ken

    And, I'm assuming you are not using a bipolar (AC) output. If you are you will need a diode in series with the base resistor.
     
    Last edited: Apr 15, 2010
  3. runningrage

    Thread Starter New Member

    Apr 14, 2010
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    What ohm resister do i need and what is bipolar AC output is that bisaing between NPN & PNP
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    The resistor value depends on the output voltage you are getting from the function generator, the transistor you are using, and the collector load resistance.

    Bipolar output means the the polarity, with respect to ground (common), reverses every half cycle. Where do you have the "FUNCTION" switch set?

    ken
     
  5. runningrage

    Thread Starter New Member

    Apr 14, 2010
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    If the transistor is work good i should get a resistance measurement of what ,and if the transistor is bad i should get 0 ohm resistance between base and emitter
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    If the transistor is bad you will get an ∞ Ω (open) or a reading at or near 0Ω (short). The resistance reading for a good transistor will vary, depending on the meter, ~1-5MΩ on my digital meters. The newer meters have a "diode" position on the resistance scale. This will show the forward voltage drop of the B-E junction (0.6-1.2V) in one direction and an open in the other.

    Ken
     
  7. runningrage

    Thread Starter New Member

    Apr 14, 2010
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    I don't have ossocillscope yet but i understand what you mean by function generator set the DC offset. How to you prevent the B-E terminal of transistor from being damage was it the voltage the damage it. Can please send reliable schmatic that would work get great for drive 3 ohm coil or would schmatic work i found here on this forum "Below"

    http://forum.allaboutcircuits.com/album.php?albumid=26&pictureid=411
     
    Last edited: Apr 15, 2010
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    No it was the current. With no current limiting resistor between the base and the function generator, the junction looked almost like a short to the generator. It supplied all the current it could, and was more than the transistor could handle.
    So you want to drive a 3Ω speaker with a single transistor amp? What's the power supply voltage to the transistor? What transistor are you using?

    I think you're at the point where you need to do a little studying on the operation of transistors. Take a look through the eBook tutorials in the tabs at the top of this forum.

    Ken
     
  9. runningrage

    Thread Starter New Member

    Apr 14, 2010
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    I need to study transistor on technical understanding thank for the advice where is the ebook is it spell ebook or something elsa
     
  10. runningrage

    Thread Starter New Member

    Apr 14, 2010
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    never mind find it
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Sorry about not being specific. Scroll to the top of the screen. There are 8 blue tabs labled: VOL. I DC...VOL. II AC...VOL. III Semiconductors....... You will find the tutorials by clicking on these tabs.

    Ken
     
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