# H-bridge with 4 N-ch FETs

#### BlackMelon

Aug 7, 2012
188
I want to design H-bridge to drive 12V DC Motor at rate of 12A with Pulse Width Modulation
but the problems is the FETs which can drive the motor with that high current are N-ch (The P-ch is so expensive because it's extremely rare in my area) so I have to put 4 N-ch FETs in the H-bridge and 12V battery to drive the motors
But the problems is how to drive the gates of FETs correctly? and how the circuit will be?
(I've got a Microcontroller which can give me only 5-0V pulse,and one 12V battery)

#### BobK

Jan 5, 2010
7,682
You need a high-side driver. They use a bootstrap capacitor to raise the voltage above V+ in order to turn on the gate even though the source is at a high voltage.

The are often packaged as a high and low in one package to drive half a bridge. There might even be full bridge drivers.

Bob

#### BlackMelon

Aug 7, 2012
188
Yes,There are full bridge drivers... but they can't withstand such a high current that I'm gonna use T___T

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
They're not designed to drive the motor, they're designed to drive the mosfets which drive the motor.

And yes, a mosfet can have a gate current measured in amps!

#### BobK

Jan 5, 2010
7,682
They're not designed to drive the motor, they're designed to drive the mosfets which drive the motor.

And yes, a mosfet can have a gate current measured in amps!
But, hopefully, only for microseconds.

Bob

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
But, hopefully, only for microseconds.

Hopefully, several orders of magnitude less than that!

#### BobK

Jan 5, 2010
7,682
Yeah, you're right, nanoseconds.

Bob

#### BlackMelon

Aug 7, 2012
188
Sorry I can't get your idea about using Full bridge drivers to drive 4FETs in h-bridge...
Plz. explain me more with the circuit diagram
Thank you

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Give me a part number. I will find the datasheet for you and show you (unless we're talking bout different things)

#### BobK

Jan 5, 2010
7,682
A full bridge driver usually means an IC that drives the motor directly. What you need is a MOSFET gate driver with high-side and low-side drivers. I think most of these come with one of each per package. I don't seem to be able to find any that have 2 of each in a package, so you will need 2 high-side + low-side driver chips to drive a full bridge.

Bob

#### BlackMelon

Aug 7, 2012
188
ok sorry for making confusions..
I think I'm gonna use chips that BobK has spoken of
but how the circuit will be?

#### BobK

Jan 5, 2010
7,682
Pick out a chip and it will have examples in the datasheet. The high-side and low-side drivers will go between your signals from the microcontroller and the gates of your power MOSFETs.

Bob

Replies
4
Views
855
Replies
1
Views
8K
G
Replies
0
Views
2K
Guest
G
Replies
6
Views
107
Replies
4
Views
741