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Why 2 n channel mosfet?
Why 2 n channel mosfet?
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Old 17th December 2020, 07:08 AM   #1
jacob117 is offline jacob117
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Default Why 2 n channel mosfet?

Hello, we are in the process of building a Class D amplifier, but why are most top end designs, using 2 N channel MOSFETS, there most be a reason why?
Cause it would be possible to use 1 N channel and 1 P channel as well.

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Old 17th December 2020, 07:38 AM   #2
drMordor is offline drMordor  Russian Federation
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Why 2 n channel mosfet?
See datasheet
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Old 17th December 2020, 07:43 AM   #3
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by jacob117 View Post
Hello, we are in the process of building a Class D amplifier, but why are most top end designs, using 2 N channel MOSFETS, there most be a reason why?
Cause it would be possible to use 1 N channel and 1 P channel as well.

Regards

Its long way to learn, if you coming from Class AB

The reasaon is because the Mosfets working as switches

and check P Channel datasheet and you get the answer


- you will need many years to learn and good Prof teacher with experience

for stable working design

- original semiconductor devices from reliable supplier not cheap 3th party

and so on

good luck, problems will come

Last edited by NMOS; 17th December 2020 at 07:53 AM.
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Old 17th December 2020, 08:12 AM   #4
jacob117 is offline jacob117
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We have checked and the datasheet of the P MOS says it can be used for switching? what else in the datasheet should suggest it cant? please explain.
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Old 17th December 2020, 10:02 AM   #5
PetruV is offline PetruV  Romania
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P channel mosfets are much weaker than N channel ones,so they use two of them,altough some simple designs use a complementary pair to make driving easier(if it's a small amp)
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Old 17th December 2020, 06:24 PM   #6
MorbidFractal is offline MorbidFractal
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Quote:
Originally Posted by jacob117 View Post
We have checked and the datasheet of the P MOS says it can be used for switching? what else in the datasheet should suggest it cant? please explain.
N-Channel Mosfets are majority carrier, electrons, devices. P-channel Mosfets are minority carrier, holes, devices.

Broadly speaking the mobility of holes is half that or electrons and as such for a given die area a P-channel device will have twice the intrinsic on resistance of an N-channel device. Look at the datasheets for an IRFNNN versus an IRFPNNN where the N's are the same.

The P-channel device will always have about twice the on resistance of the complementary N-channel device. If you want to achieve the same on resistance then you need a bigger die area perhaps twice as big but, as a result, the device capacitances also double/square and that impacts on the switching performance.

In a Class D amplifier and other applications involving a half bridge it is desirable to minimise dead time and as such it is good to have the switching characteristics of the power devices closely matched. With the advent of level shifted gate drivers that becomes an achievable goal.
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