N –channel Depletion type MOSFET (DMOSFET)
Construction
, Operation and characteristics
There are two types of static characteristics and can be explained with the operation of
the device.
1 Output or drain characteristic and
2 Transfer characteristic.
The curve drawn between drain current ID and drain-source voltage VDS with gate-to
source voltage VGS as the parameter is called the drain or output characteristic.
Transfer characteristics are drawn for ID values at different VGS values.
This device can be operated in 2 modes. They are depletion and enhancement modes.
The operation can be analyzed for
VGS = 0, VGS < 0 and VGS > 0.
1) VGS = 0 and VDS > 0
A direct connection between Gate to source sets VGS = 0, and drain to source voltage
VDS is applied between drain and source as shown in the figure below.
Now free electrons of n channel get attracted towards positive terminal of drain and
current ID starts flowing according to ohm’s law.
At constant VGS, increase in VDS will deplete the channel more at drain side as
compared to source side. Due to this current ID will saturate. At VGS = 0 current is
IDSS. (See drain characteristics figure).
IDSS is drain to source current with a short circuit from gate to source.
Fig. N-channel DMOSFET with VGS = 0 and VDS > 0
Construction
, Operation and characteristics
There are two types of static characteristics and can be explained with the operation of
the device.
1 Output or drain characteristic and
2 Transfer characteristic.
The curve drawn between drain current ID and drain-source voltage VDS with gate-to
source voltage VGS as the parameter is called the drain or output characteristic.
Transfer characteristics are drawn for ID values at different VGS values.
This device can be operated in 2 modes. They are depletion and enhancement modes.
The operation can be analyzed for
VGS = 0, VGS < 0 and VGS > 0.
1) VGS = 0 and VDS > 0
A direct connection between Gate to source sets VGS = 0, and drain to source voltage
VDS is applied between drain and source as shown in the figure below.
Now free electrons of n channel get attracted towards positive terminal of drain and
current ID starts flowing according to ohm’s law.
At constant VGS, increase in VDS will deplete the channel more at drain side as
compared to source side. Due to this current ID will saturate. At VGS = 0 current is
IDSS. (See drain characteristics figure).
IDSS is drain to source current with a short circuit from gate to source.
Fig. N-channel DMOSFET with VGS = 0 and VDS > 0
