MOSFET protection diode

[Murugesh_89]

Hi,
I am using IRF540N mosfet for switching. In datasheet they have given a diode ( like zener diode ) in the pin symbol across drain and source.

I saw some circuit with a normal pn diode symbol across the drain and source of mosfet.

Is it necessary to put a diode like 1N4007 across drain and source of IRF540N?

If i put the diode then will it be the good or harmful to the circuit?

Thanks....

 

[pradhan.rachit]

The diode is used as a protective element for the MOSFET.
It is called a freewheeling diode which is used to protect the FET from any transient voltages that are generated across it when the FET is involved in switching any inductances.
While normal conduction, this diode remains reverse biased.
When the MOSFET turns off, the magnetic field of the inductor collapses and a back emf is induced which forward biases this diode and this diode suppresses the transient.

 

[Audioguru]

The diode is used as a protective element for the MOSFET.
It is called a freewheeling diode which is used to protect the FET from any transient voltages that are generated across it when the FET is involved in switching any inductances.
While normal conduction, this diode remains reverse biased.
When the MOSFET turns off, the magnetic field of the inductor collapses and a back emf is induced which forward biases this diode and this diode suppresses the transient.

No.
The voltage across the Mosfet never reverses.
The avalanche diode on the schematic of a power Mosfet is part of its structure. It is powerful but it is slow.
A free-wheeling diode is not connected parallel to the Mosfet, instead it is connected parallel to the load.
When the Mosfet turns off the current tries to keep flowing by making the drain pin a high positive voltage which causes the avalanche diode to breakdown and conduct unless the load has a parallel free-wheeling diode to dump the power into the positive power supply.

 

[Murugesh_89]

I have the free wheeling diode across the load.

My doubt should i put a another diode (like 1N4007) parallel to drain(Cathode) and source(Anode) of mosfet..

If i put it then will be good or harmful to the circuit?

 

[godfreyl]

My doubt should i put a another diode (like 1N4007) parallel to drain(Cathode) and source(Anode) of mosfet..

No, that's not needed.

 

[pradhan.rachit]

A free-wheeling diode is not connected parallel to the Mosfet, instead it is connected parallel to the load.

Oh yes! Thank you!