Body Diode on IRLZ44N Mosfet

[amadeok]

Hello,
I'm trying to run a rather powerful dc motor (7v 2.5A) with a mosfet an a arduino. I understand that a diode is reccomended to protect from the current going back. I'm reading in the datasheet of the IRLZ44N that is has a Body Diode (page 2):

http://www.irf.com/product-info/datasheets/data/irlz44n.pdf

Will that diode protect the mosfet?
Or this? **broken link removed**
thanks

 

[Diver300]

You generally need to protect the MOSFET from overvoltage. That comes from the reverse voltage across the motor when the current it stopped by the MOSFET.

The normal way to protect the MOSFET is to put a diode in parallel with the motor. The diode blocks the current when the MOSFET turns on, and allows the reverse current from the motor to flow.

The body diode is in the wrong place to protect the MOSFET.

 

[Pommie]

The body diode is in the wrong place to protect the MOSFET.

The datasheet shows the MOSFET driving inductive loads without any additional diode. If the power supply can adequately absorb the energy then is an additional diode required?

Mike.

 

[Diver300]

The datasheet shows the MOSFET driving inductive loads without any additional diode. If the power supply can adequately absorb the energy then is an additional diode required?

Mike.

I think that the body diode is a zener diode, so that will protect the MOSFET. I don't think that energy will be absorbed by the power supply. It will be absorbed by the zener diode.

 

[audioguru]

I am glad that you do not need the no-name-brand very cheeep diodes from ebay that are probably fake.

 

[amadeok]

Hi,
Thanks for reply. I understand. However i coulnd wait for the diode to arrive. I saw some videso on youtube of people not using diodes so i thought i'd try. It works fine but as a safety measure i programmed the arduino PWM to decrease gradually over about 15 seconds. Would this have saved me if the mosfet wouldn't have had built-in protection?

 

[Diver300]

Hi,
Thanks for reply. I understand. However i coulnd wait for the diode to arrive. I saw some videso on youtube of people not using diodes so i thought i'd try. It works fine but as a safety measure i programmed the arduino PWM to decrease gradually over about 15 seconds. Would this have saved me if the mosfet wouldn't have had built-in protection?

No.
PWM is just turning on and off quite fast. There is a voltage spike due to turning off, and that voltage spike will be limited by the zener in the body diode. PWM just means that there are lots of spike instead of just one.

 

[amadeok]

No.
PWM is just turning on and off quite fast. There is a voltage spike due to turning off, and that voltage spike will be limited by the zener in the body diode. PWM just means that there are lots of spike instead of just one.

I see, so that means that the current and voltage in the drain will also be intermittent like PWM?

 

[Diver300]

I see, so that means that the current and voltage in the drain will also be intermittent like PWM?

Yes, usually. If you turn on and off really fast, in the region of MHz, then the MOSFET might not turn on and off that fast, and it will act like a variable resistor.

In normal speed PWM, in the range 1 - 50 kHz, the voltage to the motor will also turn on and off that fast. It is best to have a diode across the motor when doing that.