Urgent Reply please

Discussion in 'The Projects Forum' started by magantiamala, Aug 15, 2012.

  1. magantiamala

    Thread Starter New Member

    May 8, 2012
    25
    0
    My doubts:
    For a given Type of power MOSFET transistor:

    - How much inductive kick-back energy can it survive for a single pulse at room temperature?
    - How much at other temperature (e.g. 100°C)?
    - How much is this kick-back energy dependent on the current level?
    - How much is this kick-back energy dependent on piece part variation?

    We need an set of tests to answer the above questions. It may be beneficial to first address these questions one by one, that means define a separate tests to answer each of these questions. Later, we can look at it if it is possible to answer multiple questions with one and the same test. But this is a second step.

    The approach is like this:
    - Define the test
    - Discuss the test for benefits and drawbacks (questions answered and questions not answered)

    Here is one example:
    Test
    Benefits
    Drawbacks
    Slowly increase the inductive kick-back energy
    Can determine at which level the transistor fails
    Test applies multiple pulses to transistor, instead of single pulse


    What other tests can you think of to answer all of the above questions?
     
  2. cork_ie

    Member

    Oct 8, 2011
    348
    58
    This is like asking how fast can a blue car go.

    All mosfets are different, that is why we have things called datasheets, which describe the characteristics of the particular component.
    If you search your component number & datasheet , you will very likely find it. The datasheet should answer most of your questions. Please post again when you have the part# of your particular component and if you have more questions or if there is anything you don't understand you will get help.

    What value of inductance are you connecting to ? Kickback voltage is going to be determined (among other things),by inductance of motor or coil driven by your mosfet and the working voltage. Have you got a schematic for your circuit?
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    Agreed with cork_ie.

    Additionally, the term "inductive kick back energy" is not defined.

    What is defined is the "Maximum Safe Operating Area" which will show current vs voltage and how long their product is sustainable. The curves are for single pulse, room temperature, and typical,thus not a worst case number.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    We do know that the energy in an inductor is given by (1/2)LI^2. So a back of the envelope calculation for say a 220 mH inductor carrying 1 Ampere would be:

    (1/2)(220e-3)(1)^2 = .11 Joules

    With more current flowing in the inductor the energy goes up proportional to the square of the current. For 3 Amps in the inductor you have almost a Joule.

    That is the same energy as 220 grams moving at 3 meters/second. Do you want to stand in the way of that moving mass? Hmmm....I didn't think so.
     
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