User guide

Atlas DCA Pro User Guide December 2012 – Rev 1

Page 22

N-Ch Depletion

mode MOSFET

Red-S Green-G Blue-D

Gate threshold

(

)=-2.918V

at I

=5.00mA

Depletion Mode MOSFETs

The fairly rare Depletion Mode MOSFET is very similar to the

conventional Junction FET (JFET) except that the gate

terminal is insulated from the other two terminals. The input

resistance of these devices can typically be greater than

1000MΩ for negative and positive gate-source voltages.

Depletion Mode devices are

characterised by the gate-source

voltage required to control the drain-

source current.

Modern Depletion Mode devices are

generally only available in N-Channel

varieties and will conduct some current

between its drain and source terminals even with a zero voltage applied across

the gate and the source. The device can only be turned completely off by taking

its gate significantly more negative than its source terminal, say –5V. It is this

characteristic that makes them so similar to conventional JFETs.

Depletion mode

MOSFET

Enhancement mode

MOSFET

5.0mA