IRF540n

[samarsingla]

I using IRF540n for driving a dc motor in one directional only. I am controling speed by PWM. I tested initially without any protection diode.. and it worked fine. Please someone tel me is there any internal protection alreay there in IRF540n. If no, which diode should I use and how do I connect it?? I am a beginner and require it urgently, please help.
Thanx.

 

[Hero999]

The diode in reverse parallel with the motor isn't for protection, it for efficiency. I strongly recommend you include it.

 

[Styx]

The diode in reverse parallel with the motor isn't for protection, it for efficiency. I strongly recommend you include it.

err while protection isn't really the right word, it is kind of
the diode across the motor (which is essentially an inductor) provides a free-wheel path for the current that has build up in it via the controlled switch.

Without the diode across the motor/inductor when you goto turn the switch of (due to PWM) the inductor will develope a sufficient voltage to keep the current flowing (backEMF if you will) THAT will cause the FET/switch to hit is avalaunch voltage

 

[samarsingla]

Can you please post me a schematic for that and tell what kind of diode should i use? Are ultrafast diodes good for the purpose?

 

[Styx]

Can you please post me a schematic for that and tell what kind of diode should i use? Are ultrafast diodes good for the purpose?

OMG!!! I am not cross-replying to a cross-post!!!
use your ORIGINAL thread WHERE I have posted the cct!!!

and next time
1) USE THE SEARCH
2) DO NOT CROSS-POST

 

[audioguru]

Maybe his memory is failing so he forgot that this stuff was already discussed in his other post.
Maybe he wants another point of view from somebody else.

 

[samarsingla]

Sorry for breaking the rules of the forum. I will take care next time.

 

[Hero999]

Without the diode across the motor/inductor when you goto turn the switch of (due to PWM) the inductor will develope a sufficient voltage to keep the current flowing (backEMF if you will) THAT will cause the FET/switch to hit is avalaunch voltage

I know but even if this wasn't a problem a diode is still recommended. The diode allows the current to flow inbetween pulsses so the energy isn't wasted. Some effiecent PWM controllers use a P-channel MOSFET instead of a diode because it has a lower voltage drop.