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Linear Regulator, Surge Protected to 200V VIN using Depletion Mode MOSFET. A much simpler solution is to use a Depletion-mode MOSFET, as shown in Figure 9. The gate of the depletion FET, a DN2625, is connected to VOUT. The source is connected to the input of the LDO, LM2931.
Depletion MOSFETs, unlike enhancement MOSFETs, are in an on-state even at 0 V of gate-to-source voltage (VGS). This feature makes them suitable for using as a constant current source as well as in other ways. This application note explains how depletion MOSFETs can be used in different applications.
22 lis 2022 · The only difference is whether the conductive channel is absent at zero gate voltage (enhancement-mode) or present at zero gate voltage (depletion-mode). You can even build a MOSFET that's somewhere between enhancement-mode and depletion-mode with a threshold voltage of exactly zero volts.
20 kwi 2020 · An enhancement MOSFET is by definition “off” when there is no gate voltage, or when V GS is 0. In contrast, a depletion mode MOSFET is “on” when there is no gate voltage, it is naturally in a conducting state.
1 cze 2016 · If you do it with a depletion fet, it is very easy: basically, you just have to set its source to the supply pin of the controller, the gate to the ground of the controller, and the drain to the high voltage (this is a simplified view):
To turn on an N-channel Depletion-type MOSFET, to allow for maximum current flow from drain to source, the gate voltage should be set to 0V. When the gate voltage is at 0V, the transistor conducts the maximum amount of current and is in the active ON region.
For a depletion mode NMOS FET, with 0 V gs the channel will conduct. V gs must be pulled below 0 V in order to cut off the channel. In SPICE this behavior is represented by a negative threshold voltage, controlled by the VTO parameter.
