MOSFET AS A SWITCH

[Muhammad Owais]

i want to use mosfet as a switch then in which mode i operate it linear or saturation........!!!

 

[rumpfy]

saturation

 

[audioguru]

If you read a detailed description of a Mosfet then its Saturation and Linear modes are the opposite of a bipolar transistor.

A bipolar transistor is Saturated when it is turned on like a switch, a Mosfet is Linear when it is turned on like a switch.
A bipolar transistor is Linear when it is partially turned on and is amplifying, a Mosfet is Saturated when it is partially turned on and is amplifying.

To turn on a Mosfet like a switch then its gate to source voltage must be as high as is shown in its datasheet. Most Mosfets need 10V to completely turn on but Mosfets called "logic Level" need only 4.5V.

 

[Muhammad Owais]

if i want to use mosfet in a h bridge using ir2110 in which mode does the mosfet should operate linear or saturation ??

in linear region mos behaves like a resistor so should we use mos in linear region ...........and in which region the mosfet has the lowest Vds.

 

[rumpfy]

saturation

 

[Reloadron]

The IR2110 is a MOSFET driver:

Description
The IR2110/IR2113 are high voltage, high speed power MOSFET and
IGBT drivers with independent high and low side referenced output channels.
Proprietary HVIC and latch immune CMOS technologies enable
ruggedized monolithic construction. Logic inputs are compatible with
standard CMOS or LSTTL output, down to 3.3V logic. The output
drivers feature a high pulse current buffer stage designed for minimum
driver cross-conduction. Propagation delays are matched to simplify use in high frequency applications. The
floating channel can be used to drive an N-channel power MOSFET or IGBT in the high side configuration which
operates up to 500 or 600 volts.

You want to drive your H Bridge MOSFETs into saturation. Just make sure this driver is compatible with the MOSFETs you plan to drive.

Ron

 

[shortbus=]

Here we go again. This question comes up from time to time, mosfet as switch saturation/linear. And confuses me and others. Guru says switch = linear. Rumpfy and reloadron say switch = saturated. From the little I know, I'd say Guru is correct, mosfet as switch = linear region. Anyone else want to chime in?

 

[audioguru]

Simply read about Mosfets in Google. I learned about Mosfets from applications notes at International Rectifier Corp www.irf.com .

 

[Reloadron]

Here we go again. This question comes up from time to time, mosfet as switch saturation/linear. And confuses me and others. Guru says switch = linear. Rumpfy and reloadron say switch = saturated. From the little I know, I'd say Guru is correct, mosfet as switch = linear region. Anyone else want to chime in?

Guru is correct in what he posted. Right on target correct. That said here is why I replied the way I did and agreed with rumpfy. There was actually a logic and some thought to my reply. Granted not much but some.

i want to use mosfet as a switch then in which mode i operate it linear or saturation........!!!

Reading this original question as it was posted and then reading AudioGuru's fine reply:

If you read a detailed description of a Mosfet then its Saturation and Linear modes are the opposite of a bipolar transistor.

A bipolar transistor is Saturated when it is turned on like a switch, a Mosfet is Linear when it is turned on like a switch.
A bipolar transistor is Linear when it is partially turned on and is amplifying, a Mosfet is Saturated when it is partially turned on and is amplifying.

To turn on a Mosfet like a switch then its gate to source voltage must be as high as is shown in its datasheet. Most Mosfets need 10V to completely turn on but Mosfets called "logic Level" need only 4.5V.

With AudioGuru's post in mind I would suggest the OP read the link AG posted or even something like this link. Unfortunately I start questioning the OP's ability to grasp and understand either link, which granted is sort of stupid on my part. However, since a MOSFET is a transistor as the T in MOSFET implies I just said saturation and let it go at that. Just seemed simple at the time but granted incorrect. I should have said "Linear" and let the OP figure it out I guess. Considering Linear is the correct answer. So if the OP wants to use MOSFETs in a H Bridge configuration to turn a motor on and off and reverse direction the MOSFETs will be operating in their linear region when acting as switches.

When questions like this arise I really shouldn't over think and just post an answer like AG did and let it go at that.

Ron

 

[audioguru]

Because the modes of a Mosfet are confusing then I never say it is saturated or is linear. Instead I say it is amplifying or it is switched on.

 

[Mosaic]

Is this because MOSFETs are voltage based switches and bipolars are current based switches?

 

[Reloadron]

Because the modes of a Mosfet are confusing then I never say it is saturated or is linear. Instead I say it is amplifying or it is switched on.

I like that answer.

Ron