MOSFET Switching Network Suggestions Help

Discussion in 'General Electronics Chat' started by cebucher, Apr 25, 2013.

  1. cebucher

    Thread Starter New Member

    May 27, 2012
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    Hey all -

    I am trying to figure out the best (simple/low cost) option for implementing the S1 and S2 switching network in the attached circuit. I would like to switch them from a low cost micro-controller with 5V output if possible. The switches should always be complementary to one another. I would like to use either MOSFETs or Transistors.

    Any design suggestions would be greatly appreciated.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Is there any particular speed requirement?

    What's the current requirement?
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    So what does those 200mA have to do with all this? And how do you expect two simple swithces to convert 150V to 50V?
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Didn't you see the "black box"?:p
     
  5. #12

    Expert

    Nov 30, 2010
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  6. cebucher

    Thread Starter New Member

    May 27, 2012
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    Hello - thanks for the posts.

    I do not have any specific speed requirement (for simplicity, lets say 1000hz). The current I would like to switch is up to 200ma.

    The black box is what actually converts the voltage, but requires the switching network of S1 and S2.

    I am having trouble understanding how to use MOSFETs in place of S1 and S2 to do the switching and how to use a microcontroller 5v output to control the gate of the MOSFETs. It looks like I can do it by using a an NPN transistor to control the gate of the MOSFET, switching from 150 volts to ground and using a pull up transistor to control the gate of the MOSFET, but doesn't seem like a good way. I was hoping someone may have some good examples of controlling these fairly high voltage devices from a microcontroller.

    Thanks
     
  7. crutschow

    Expert

    Mar 14, 2008
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    The black box converts what voltage?
    Does the black box generate the voltages to be connected to 50V and 150V loads?
    Is that load voltage zero when its associated switch is open?
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    I drawn the circuit, you guys just point the bug and make it better.

    [​IMG]
     
    Last edited: Apr 27, 2013
  9. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Well, the 2n3904 can't handle 150 volts, should use a TR rated at 200 volts or more.
    The mosfet's maximum gate-source voltage appears to be 30 volts, so a zener diode should be added across the g-s along with a series gate drive resistor.

    Fet2 drain source are drawn backwards, and it might be a good idea to add series diodes from each supply "pointed" towards the black box supply input in case both supplies are accidentally turned on at the same time. ;)
     
    Last edited: Apr 27, 2013
  10. cebucher

    Thread Starter New Member

    May 27, 2012
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    Scott - thank you very much for the drawing.
    Tableguy - thanks for your review and suggestions.

    I will give it a try under simulation.
     
  11. ScottWang

    Moderator

    Aug 23, 2012
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    The circuit :

    [​IMG]
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    Thanks tubeguy.
    The op doesn't define the black box clearly yet, so we only can guess what the box function is.

    The 2n3904 bjt that I only calculate the current that shall be ok, but I forgot the voltage also will be affected.

    I'm already used the transitors to control it and to avoid it to happend like two mosfets turn on at the same time, but I can't say that it won't happend, and I'm agree with you to add some parts to protect the parts.

    The new circuit :

    [​IMG]
     
  13. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Tableguy ? I do like to eat ... how'd you know ? :p

    Yes, Scott thanks for the drawing. Of course D2 and FET2 need to be reversed. ;)
     
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