Help with this totem pole mosfet driver circuit.

Discussion in 'General Electronics Chat' started by jdraughn, Dec 22, 2010.

  1. jdraughn

    Thread Starter Active Member

    Jan 30, 2009
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    I am trying to build a simple totem pole driver using transistors. I HAVE had it working using a single transistor to fully saturate the mosfet. It's an IRF510 mosfet.

    I am using the circuit show in the first post here: http://forum.allaboutcircuits.com/showthread.php?p=177826

    Right now I am just using 5v all around since i'm testing with an led, and the problem is that when I send 5v to the enable line, my led lights up nice and bright, but when I remove power from the enable line, instead of the led turning off, it just dims to about half brightness. Grounding the enable line makes no difference.

    If I replace the mosfet with an led, the led turns fully off and on as expected, which leads me to believe the problem is with my mosfet.

    Using a single transistor I had the mosfet sending 12v to a motor and I noticed no change in temperature of the mosfet. Did I somehow burn it up between single transistor and totem pole driver circuit? I was always very careful to make sure that all the pins where stuck in antistatic foam or all connected to ground until I plugged it right into my circuit.

    I will try the single transistor setup again and see if it appears to still work.
     
  2. jdraughn

    Thread Starter Active Member

    Jan 30, 2009
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    Looks like the single transistor setup doesn't work anymore either, same problem where the mosfet still conducts even if I have the gate grounded. This is the second 2.00 radio shack mosfet I have burned up, and I don't know how im burning them up. After burning up the first one I was even more careful this time, even though I was pretty dang careful the first time too. I have some better/cheaper ones coming in the mail but I don't want to start burning those up too.
     
  3. Kermit2

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    Feb 5, 2010
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  4. Kermit2

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    Feb 5, 2010
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    [​IMG]


    Is this the circuit you have constructed?

    Is everything correct? as shown in value?
     
  5. jdraughn

    Thread Starter Active Member

    Jan 30, 2009
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    Similar, but there are some differences. I tried adding a pull down resistor like your schematic has. I will try your version when I get my mosfets in the mail.

    I placed the order yesterday, priority mail, but seeing as how everything is closed on friday and saturday, I don't think I will be lucky enough to get them by thursday, so it will have to wait till monday unless I spend another 2.00 for another test fet from radioshack.
     
  6. Kermit2

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    I posted that from the thread you linked to in the post at top. You said the schematic for your circuit was in that thread.


    It is NOT my circuit design
     
  7. jpanhalt

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    Jan 18, 2008
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    You are trying to drive the gate of an IRF510 with only 5V. It's not turning on completely and is therefore burning up.

    John
     
  8. Kermit2

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  9. jpanhalt

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    The IRLZ series, e.g., IRLZ44, might be more appropriate for TH and cheap logic-level device. You may find it in surplus markets, but probably not at RadioShack.

    John
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    MOSFETs in general require 10V on the gate to turn fully on, to use less you need a logic level MOSFET, a totally different animal. Just repeating what jpanhalt said a different way.

    [​IMG]

    You need a low value resistor (10Ω - 47Ω) on the gate to keep ringing under control.

    LEDs, 555s, Flashers, and Light Chasers

    Chapter 10 - Transistor Drivers

    This goes through quick and dirty explanation how to use MOSFETs and BJT transistors.
     
  11. jdraughn

    Thread Starter Active Member

    Jan 30, 2009
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    I'm only driving an led though. Once I had it working with the led, I was going to change it to 12v and use a larger resistor on my led, and if that still worked good, then I was going to put the motor on it.
     
  12. jdraughn

    Thread Starter Active Member

    Jan 30, 2009
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    Sorry, I meant the first post in the second page (the actual page I linked).
     
  13. Kermit2

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    It would be better if YOU would post a picture of the exact schematic you are using. There are several different ones on that thread yo reference and not everyones computer displays the same number of replies per page. The post does not have a second page when I view it on this computer.
     
  14. jpanhalt

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    Jan 18, 2008
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    Well, if you are only driving an LED with the gate drive, how did you burn out the mosfet? Its gate would not be connected. Of course, if the gate were left floating, then it may turn on partially just through static.

    John
     
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