[Help] Mosfet motor control circuit problem

Thread Starter


Joined Feb 27, 2009
i'm using IRF540N to build a h-bridge.
I try to practical build the h-bridge circuit but the result same as the simulation1 (shown in the picture).

So what's problem with the circuit? why i can't get 11-12v at the output instead of 5v only?



Joined Dec 20, 2007
The gate of an IRF540 Mosfet mut be 10V more positive than its source to be completely turned on. Your lower Mosfet on the right side has only 5V and your upper Mosfet on the left side needs +22V on its gate for its source to be near 12V.

Use a Mosfet driver IC that boosts the voltage to the gates of the upper Mosfets or use P-channel Mosfets for the upper ones.

Why is your schematic a negative pic that is covered in dots?

Thread Starter


Joined Feb 27, 2009
I'm using Multisim2001 to simulate the h-bridge circuit
the background is black because it's default colour:)

+22v? in order to turn on gate?
according the datasheet, Vgs(th) = 2v to 4v
why it need high voltage to turn the gate on?

In case this only way to turn on the mosfet,
my power source is limited,
how do i modify this circuit in order to be controlled by microcontroller?


Joined May 16, 2005
The IRF540N needs 2 to 4 V between source and gate in order to begin conducting. It needs at least 7 or 8 V between source and gate to conduct fully.

If you can obtain a logic-level input bootstrapping MOSFET driver, such as the ADP3417 or the SI9910 or some such, you can use the supply and signal source you have now.

Thread Starter


Joined Feb 27, 2009
Full bridge mosfet driver chip is not cheap...
Let say if i want avoid using mosfet driver,
what model of mosfet using logic 5v to turn on?
RFD3055? is this okie?