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I was looking at the MOSFET switching characteristics and stumbled upon this video

Around 8:00 of the video, the author explains that the once the threshold voltage of the MOSFET is reached, the voltage at the gate of the MOSFET does not increase. He says the voltage is clamped because the current flows through the Gate-Drain Capacitor.

I am finding difficulty in this section alone. Why should a lot of current flow through the Gate Drain capacitor or like, what causes the current flow through that capacitor during that stage. Can someone please help me with this understanding? And if the current flow direction is also indicating that the current flows through the Gate-Drain capacitor and to the Vdd supply? So, it doesn't flow through the load but only to Vdd - Why?

Request someone to clarify.

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  • \$\begingroup\$ The path of current flow at the Miller Plateau isn't to Vdd, it goes through the drain-source channel (which has just formed at this point). \$\endgroup\$
    – Hearth
    Commented Jun 26, 2021 at 18:26
  • \$\begingroup\$ Thank you. But why does the current flow causing Miller Plateau ? \$\endgroup\$
    – user220456
    Commented Jun 26, 2021 at 18:30
  • \$\begingroup\$ Because the drain voltage is dropping and Cdg needs to be charged. \$\endgroup\$
    – Hearth
    Commented Jun 26, 2021 at 18:30
  • \$\begingroup\$ I am finding difficulty over here only. If the other plate of the capacitor (connected to Vdd) , the voltage is dropping, why should there be more current flowing into the opposite plate of the capacitor? \$\endgroup\$
    – user220456
    Commented Jun 26, 2021 at 18:32
  • \$\begingroup\$ What happens when the drain voltage drops below the gate voltage? That part should be straightforward enough. Now consider how the voltage across the capacitor changes during that time, and what causes that change. \$\endgroup\$
    – Hearth
    Commented Jun 26, 2021 at 18:32

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The gate capacitance is always there and does not suddenly occur when the threshold voltage is reached. The capacitance cannot clamp the gate voltage because the capacitor continues charging. Use a low enough value for the series gate resistor to charge that capacitance in the time delay that you want. NEVER use the threshold voltage for anything since that is the voltage that some Mosfets are barely turned on, they are almost turned off.

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