Modified switching device model

The input (gate-source) circuit of a MOSFET is simply illustrated by a capacitor The output (drain-source) circuit is expressed by an equivalent resistor and a capacitor The resistance of the equivalent resistor R  

In a high-voltage region (Vcs Vif), the lo-Vcs characteristic can be expressed by the following linear equation  

In a low-voltage region (VQs Vif), the characteristic is approximated by a quadratic function  

The coefficient fl is obtained by a condition in which the both curves are in contact at Vqs=Vih- 

The on-resistance taken from the data sheet of the MOSFET is shown in Table 4.7. 

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