what are the applications of depletion type and enhancement type MOSFET?

Thread Starter

Babun Pal

Joined Jul 13, 2016
17
Hi,

I've gone through the material on Depletion type MOSFET and Enhancement type MOSFET. I have few douts:

1). What are the applications of depletion type MOSFET e.g. Can it be used as a trans-conductance amplifier?
2) What are the applications of enhancement type MOSFET e.g. Can it be used as a switch?


Would you be kind to clarify these doubts.

Thank you.
 

Papabravo

Joined Feb 24, 2006
14,464
The easiest way to think about them is that a depletion mode device will be ON with no bias voltage between gate and source. You have to bias the gate negative with respect to the source to turn it off. An enhancement device is OFF with no bias voltage between the gate and the source, and you have to apply a positive bias to the gate to turn it on. Both kinds of devices can be used as switches, amplifiers, oscillators and such.
 

Thread Starter

Babun Pal

Joined Jul 13, 2016
17
The easiest way to think about them is that a depletion mode device will be ON with no bias voltage between gate and source. You have to bias the gate negative with respect to the source to turn it off. An enhancement device is OFF with no bias voltage between the gate and the source, and you have to apply a positive bias to the gate to turn it on. Both kinds of devices can be used as switches, amplifiers, oscillators and such.
Thank you
 

dl324

Joined Mar 30, 2015
11,593
Could you please site an example where depletion type MOSFET is used?
Information is readily available on the internet. Here's an appnote and another.

I didn't notice them mentioning that depletion mode MOSFETs can have current increased above the zero bias current by applying an appropriate gate voltage; positive for NMOS depletion mode. They are rarely used. I have never used a discrete depletion mode device and the ones used in IC design were only for decoupling caps.
 

Thread Starter

Babun Pal

Joined Jul 13, 2016
17
Information is readily available on the internet. Here's an appnote and another.

I didn't notice them mentioning that depletion mode MOSFETs can have current increased above the zero bias current by applying an appropriate gate voltage; positive for NMOS depletion mode. They are rarely used. I have never used a discrete depletion mode device and the ones used in IC design were only for decoupling caps.
Thank you.
 

ian field

Joined Oct 27, 2012
6,539
Hi,

I've gone through the material on Depletion type MOSFET and Enhancement type MOSFET. I have few douts:

1). What are the applications of depletion type MOSFET e.g. Can it be used as a trans-conductance amplifier?
2) What are the applications of enhancement type MOSFET e.g. Can it be used as a switch?


Would you be kind to clarify these doubts.

Thank you.
A depletion JFET is very similar to a thermionic triode with scaled down voltages. If you know how to auto-bias a triode - you've got the procedure for a depletion JFET.

The enhancement MOSFET is easier to use as a switch - just operate the gate at either above or below VGSthr. It can be run in linear mode with plenty of nfb to stabilise the operating point.

Most VHF/UHF FETs are depletion MOSFETS and a few specialty manufacturers do power depletion MOSFETs.
 
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