MOSFET gate charge

lauboonchong

Joined Feb 23, 2022
1
Hi, I want to calculate the rise time of MOSFET. Below is the charge information from the MOSFET datasheet.

May I know what is the difference between Qg(on) and Qgs + Qgd. The total input charge require is Qgs + Qgd or the sum of the three charges? Thank you.

LowQCab

Joined Nov 6, 2012
3,580
The Turn-On or Turn-Off Time will depend on the surrounding Circuitry.

I create a Circuit in my Circuit-Simulator using a FET-Model
that does not include the 3-Capacitance-Values,
then add the 3-Capacitance-Values as individual Components,
then run the simulation and look at the resulting wave-forms.

Usually this is only critical when using very high Frequencies.

Do You actually need to make your calculations using "Stored-Charge-Values" ?
.
.
.

MrAl

Joined Jun 17, 2014
10,898
Hi, I want to calculate the rise time of MOSFET. Below is the charge information from the MOSFET datasheet.

View attachment 302980

May I know what is the difference between Qg(on) and Qgs + Qgd. The total input charge require is Qgs + Qgd or the sum of the three charges? Thank you.
Hello,

I assume you are familiar with the basic waveforms when turning on a MOSFET.

Qgs is responsible for the initial part of the rise before the MOSFET actually starts to turn on where the rise is fairly steep.
Qgd comes into play as the MOSFET is turning on and is responsible for the nearly horizontal part of the rise.
Qg is considered over the entire rise.

See diagram.

Attachments

• 6 KB Views: 5

crutschow

Joined Mar 14, 2008
33,346
Do You actually need to make your calculations using "Stored-Charge-Values" ?
How else would you calculate the MOSFET rise and fall times when used as a switch?

shortbus

Joined Sep 30, 2009
10,038
Below is the charge information from the MOSFET datasheet.
I'm just a amateur at electronics, seemingly like you are. Something that helps me are Application Notes or App notes. All of the companies making things for electronics have them, you should learn to look for them when you have questions like this. They will help with understanding things in the data sheet and about electronic components in general.

Here is a quick Google search for mosfets as a way to show what I am talking about -