high side mosfet switching

Discussion in 'General Electronics Chat' started by sharmilla, Nov 3, 2008.

  1. sharmilla

    Thread Starter Member

    Nov 3, 2008
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    Dear all,

    Attached is a circuit to drive a single high side mosfet, the circuit works fine. but when a filter capacitor(470uF/450V) is connected to the load the IR2110 high side driver burns.

    Can any one advise on switching a high side mosfet where a filter capacitor is included at the load.


    Many thanks
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    How fast and how often does the mosfet switch?
    What exactely does the filter filter? (nicely put :))
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I wonder if it is the momentary short to ground when the capacitor is initially put in the circuit? Is the problem cured with a small resistor in series with the capacitor?

    BTW, I have a little experience with the 2110, but not with it driving a capacitative load, so this answer is mostly guesswork.

    John
     
  4. sharmilla

    Thread Starter Member

    Nov 3, 2008
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    the mosfet switch at 10Khz.
    the purpose of the 470uf /450V capacitor is as a filter to the output
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
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    First thing I noticed was your gate diode is backwards, so your turn off time will be slower than predicted. 20 Ohms is too high of a gate resistor, try 4.7-10ohms with that kind of current driver.

    I'm not really sure of anything else. Clearly by adding the capacitor, you are increasing the Vs voltage. The datasheet specs that Vs cannot be greater than 0.3+Vb, but I am not sure how the Vb is derived anyways.

    Steve
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I just came across this discussion by Linear of high-side mosfet switching for capacitive loads. About halfway down, it mentions the need to actively turn off/drain the load. Maybe you could use your low-side drive for that?

    John
     
  7. sharmilla

    Thread Starter Member

    Nov 3, 2008
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    hi is it something like this as attached.

    many thanks
     
  8. scubasteve_911

    Senior Member

    Dec 27, 2007
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    Sometimes I feel invisible... Diode to gate in backwards.. lalalala
     
  9. sharmilla

    Thread Starter Member

    Nov 3, 2008
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    owhh im very sorry scubasteve_911,:)

    actually the connection of diode to gate should be in that direction, wouldn't it short the IC if it is in the backward direction:confused:
     
  10. scubasteve_911

    Senior Member

    Dec 27, 2007
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    It's okay :p

    I believe the diode is not necessary here anyways. It's purpose is to make a symmetrical gate drive with an asymmetrical driver. For example, when the driver can sink more than source current, so it would be in the best interest to increase flow in one direction (sometimes diode in series with another resistor).

    Steve
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    Why you dont connect this MOS as a low side driver which easier to control? Is there any reason?
     
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    @Steve:

    I believe you are/were right. The diode is usually used to speed up turn off of the mosfet gate. See page 14 here.

    @Sharmilla,

    If you can't get the link, let me know, and I will copy it here. Here is the schematic from it, which is essentially what you drew (left circuit).

    Also, see AN978 from IR, which goes into more detail about Vs and Vb.

    John
     
  13. scubasteve_911

    Senior Member

    Dec 27, 2007
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    I was wrong in the reasoning for the diode, it has to do with recovery speeds and stuff. Another example when intuition is incorrect in engineering, since it isn't really natural :(

    Steve
     
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