### Author Topic: [Help] IRF540 mosfet motor control circuit problem  (Read 11557 times)

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#### onichi

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• Posts: 4
##### [Help] IRF540 mosfet motor control circuit problem
« on: February 28, 2009, 12:25:03 AM »
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?

#### Soeren

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##### Re: [Help] IRF540 mosfet motor control circuit problem
« Reply #1 on: February 28, 2009, 09:28:23 AM »
Hi,

Your problem is, that the gate of an N-ch. MOSFET needs to have its gate-pin positive a certain voltage in respect to the source-pin to open (in case of the IRF540, slightly over 4.5V) to open.
Also, if you look at it dynamically, you need to supply a good bit of current, to the gate to get it through the Miller plateau in a short time - 71 nC (nano-Coulomb) needs to be filled into the ~2nF input capacitance, when using the IRF540.

Simulators often give you false results. In a real life circuit, you'd probably get less than about 1V.
To get 12V, you need around 17V on the gate of Q1 and if you want it to do anything usefull, you need to lower the gate resistors considerably.
For a discreet build of an H-bridge to work without the gate voltages above the main circuit voltage, you need to use P-ch. MOSFETS.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Engineering is based on numbers - not adjectives

#### onichi

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##### Re: [Help] IRF540 mosfet motor control circuit problem
« Reply #2 on: February 28, 2009, 09:20:59 PM »
are you means that all the N-ch mosfet have to be changed to P-ch mosfet?
or change high side with p-ch mosfet?

• Supreme Robot
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##### Re: [Help] IRF540 mosfet motor control circuit problem
« Reply #3 on: March 03, 2009, 06:00:26 AM »
You have four MOSFETs . . . the top two must be PNP, the bottom two must be NPN.

And you don't really need the gate resistors, but you *do* need flyback diodes on each MOSFET.

Depending on what you are doing, you might also want MOSFET driver ICs . . .

#### onichi

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• Posts: 4
##### Re: [Help] IRF540 mosfet motor control circuit problem
« Reply #4 on: March 04, 2009, 10:01:15 AM »

The mosfet I used already has embedded body diode...

Let said i need a mosfet driver IC, what model of mosfet driver IC is suitable?

And then, i still have another suggestion which is change all mosfet to logic mosfet
but the problem is which model of p-ch and n-ch logic mosfet i should use?

#### ArcMan

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##### Re: [Help] IRF540 mosfet motor control circuit problem
« Reply #5 on: March 05, 2009, 04:23:45 PM »
The mosfet I used already has embedded body diode...

Let said i need a mosfet driver IC, what model of mosfet driver IC is suitable?

Those embedded diodes do not perform well for transient voltage suppression.  I don't yet know why that is, it just is.  The Open Source Motor Controller (OSMC) uses 1.5KE51CA TVSs for transient suppression.  If you look at their v3.22 design (the latest working design), do note that they forgot to add them to the high side.  They should indeed be there.

The OSMC design uses the HIP4081A as the MOSFET driver.  It is a charge-pumped high and low side full bridge driver, which allows you to use N-channel MOSFETs on the high side (which is preferred due to their low Rds ON).  This chip is obsolete and has been known to cause problems (I've had some problems with it myself).  You can still buy it at Newark Electronics, though.  I'm trying to locate a replacement for it.  I found it last week but didn't write myself a note.  I'll follow up when I find it.

#### onichi

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##### Re: [Help] IRF540 mosfet motor control circuit problem
« Reply #6 on: March 05, 2009, 11:15:30 PM »
what problems will be facing by using HIP4081A?

#### ArcMan

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