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  • Author Author: mcollinge
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Measuring a MOSFET’s Miller Plateau -- Workbench Wednesdays 25

 

 

Turning on a MOSFET takes more than knowing the threshold voltage. A special event occurs when a FET turns-on, which is called the Miller Plateau. The gate voltage sticks to the threshold voltage while the drain opens up. In this video, James shows how to measure the Miller Capacitance, using an oscilloscope and custom MOSFET test board.

 

Supplemental Content:

 

 

Bill of Material:

 

Product NameManufacturerQuantityBuy KitBuy Kit
FQP30N06LFQP30N06L - Power MOSFET, N Channel, 60 V, 32 A, 0.027 ohm, TO-220AB, Through HoleOn Semi1Buy NowBuy Now
Arduino UnoArduino1Buy NowBuy Now
1 GHz Active Probe RT-ZS10Rohde & Schwarz2Buy NowBuy Now

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    Would have really liked to see the results with different resistor values.

    That was my original plan. But I got totally fascinated with such a clear demonstration of the plateau. Maybe it is something that can be covered more in the future.

    Does rise and fall times listed in the datasheet coorelate completely with the input and output capacitance? What other things would you consider for rise and fall times to optimize switching speed? Look forward to a follow up video on this subject

    I think the gate's forward transconductance is probably a better way to estimate the rise time for the turn-on. From what I understand, it will vary based on the drain's current. I would expect layout and trace parascitics to have more significant impact though.

  • Great presentation JL. If you were to offer a suggestion on gate resistor what would that be. I know it's device dependent for optimal but venture a guess for close?

  • in reply to baldengineer

    You did a good job of that.

     

    The reference to the work Karen is doing will hopefully get more people to view her videos.

    She does a very good job of introducing the technology.

     

    DAB

  • I think these modules that get into some of the more subtle characteristics of components are fascinating. is always doing nice deep dives into component characteristics. Thank you for your Work Bench Wednesdays. I am looking forward to any expansion on the MOSFET topic.

     

    John

  • in reply to DAB

    Thanks DAB. After doing these measurements, my next step is to build a (low voltage) push-pull output stage, to show how shoot-through happens. Which would also be a good time to discuss turn-on versus turn-off time.

     

    With this video, I wanted to test the waters of an episode that is a mix of Learning Circuit and Workbench Wednesdays.

  • Another great episode.

     

    I would just add that those switching delays can add up in complex circuits requiring a careful timing analysis on your circuit to keep interesting effects developing.

     

    DAB