how to select mosfet

[mdkmahesh]

alex, i need mosfet for higher voltage means in the range of 230 to 320V but the IRF540 is for 100V only.Because at the time of starting my entire voltage may appear across mosfet ,so we have to provide a mosfet with higher voltage

 

[alexan_e]

This is the first time you mention the voltage specification for the mosfet, I haven't done any project with high voltage so I haven't used any such mosfet.
I did a search and IRF740 (400v/10A) can work but the on resistance is 0.55 ohm so the losses on the mosfet would be higher that the previously mentioned mosfets.
I'm sure there are mosfets with much lower Rds-on but there would probably be more expensive.

Alex

 

[kalaianand]

IRF 450 is also an good choice. 500V, 13A.
while selection process also look into the other parameters....

 

[mdkmahesh]

in specifications i seen that ID @ TC and TA...what is the difference between them

 

[alexan_e]

Tc is the case temperature and when it gets higher the max current lowers.
Ta could be ambient temperature but it is usually Tamb, where did you read it?

Alex

 

[kalaianand]

in specifications i seen that ID @ TC and TA...what is the difference between them

Always remember

Ta - Ambiant temerature
Tc - Temperature of surface of the selected IC package
Tj - Junction temperature

---------- Post added at 12:27 ---------- Previous post was at 12:25 ----------

The manufacturers mention the Tc value.
ID @ Tc means, when specified ID current flows into the device, the device surface will reach specified Tc value.

Hope its usefull

 

[alexan_e]

The manufacturers mention the Tc value.
ID @ Tc means, when specified ID current flows into the device, the device surface will reach specified Tc value.

Didn't it seem strange to you that the manufacturer gives a lower current with a higher Tc, How can a lower current heat the device more?

Actually the specification says exactly the opposite, it is like this

ID Drain Current (continuous) at Tc=25 degree 10A
ID Drain Current (continuous) at Tc=100 degree 6.3A

The maximum current that can be used without damaging the device is specified according to the case temperature.

Alex

 

[mdkmahesh]

So for my application,requirements of MOSFET (VDSmax=320V,ID=3A and low RDS(on)) IRF 740 is best option wright?

 

[alexan_e]

IRF450 that was also suggested has a lower on resistance (0.4 ohm ) but the datasheet shows a TO3 case which will probably not be convenient to use.
There are many models that could be used but IRF740 (TO220 case) would work fine for your application and can handle more current and voltage that your specification, It is cheap and you should be able to find it easily.
The power consumption on the mosfet will be about 5W with 3A load, If you find it high then there are mosfets with lower on resistance but probably more expensive and I don't know which ones will be available in your area.

Alex