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Does FET (D-S on) voltage same to the gate cutoff voltage (VGS(off))?

Latest Updated:10/01/2010

Question:

Is it correct to consider that the voltage at which the FET turns on (D-S on) is equal to the gate cutoff voltage (VGS(off))?

Answer:

The gate cutoff voltage is the gate-to-source voltage at which the FET switches off and occurs under the conditions shown in the electrical specifications table below. (That is, the FET switches off at VGS when ID falls below the value indicated in the Conditions column.)



The on-voltage, on the other hand, is the gate-to-source voltage derived from the transfer characteristics (see the graph below). This voltage differs depending on the drain current (ID) level at which the FET turns on, which is specified by the customer. (The FET turns on at VGS when ID exceeds a certain value.)



If the drain current required by the system to turn the FET on is the same as the drain current specified in the gate cutoff voltage conditions, then the voltage at which the FET turns on (D-S on) is equal to the gate cutoff voltage (VGS(off)). However, since these drain current values are not usually the same (it requires a large current to turn most of system on), D-S on almost differs from VGS(off).

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Power MOSFETs
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