Is one manufacturers IRFP240 the same as anothers? - diyAudio
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Old 10th October 2005, 05:10 PM   #1
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Default Is one manufacturers IRFP240 the same as anothers?

I've searched the forum and can't seemto find the answer. Is there any difference between different manufacturers "IRFP240" FETs? For example here is the actual IR part :

http://www.digikey.com/scripts/DkSea...346147&Site=US

and here is a Fairchild IRFP240 :

http://www.mouser.com/index.cfm?hand..._pcodeid=51229

Thanks,

--Chris
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Old 10th October 2005, 05:25 PM   #2
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There are lots of differences, just compare the two data sheets. They are pretty interchangeable though, hence the same type number.
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Old 10th October 2005, 05:40 PM   #3
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I must add: They _may_ be interchangeable. This is dependent of your design, so once again you'll have to read the datasheets carefully and you must be aware of undocumented properties.
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Old 10th October 2005, 05:59 PM   #4
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Looking at the two data sheets the parts look almost identical. The Fairchild has lower output capacitance and higher forward-transconductance.. Aren't both these desirable properties?

--Chris
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Old 10th October 2005, 06:12 PM   #5
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Yes.
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Old 10th October 2005, 06:38 PM   #6
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Lotsa diffs..

Significant ones:

IR device EAS of 510 mJ vs FC at 250 mJ.

IR is capable of absorbing more energy in reverse breakdown, single pulse. Most likely, this is due to IR's better guardring design. Typical hits: no snubber switching, or inductive kickback.

Thermal resistance...FC better at .69 vs IR .83. I would guess FC is larger die.

The FC device looks a bit slower...on off delays and rise..

IR has 20 volt gate capability...FC at 30. FC has thicker oxide.

Transfer characteristics...IR has zero TC crossover at about 6.5 volts, FC is about 5.5 volts. Affects paralleling stability in linear or switching apps.

Cheers, John
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Old 10th October 2005, 07:03 PM   #7
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Jneutron,

Thanks for looking at the DS!

These will be used in a class A audio amplifier so isn't it safe to assume the mosfet should always be on so the on/off rise time will not be detrimental?

Better thermal resistance =

About the zero crossing, could you elaborate on what you wrote :

Transfer characteristics...IR has zero TC crossover at about 6.5 volts, FC is about 5.5 volts. Affects paralleling stability in linear or switching apps.

I'm not very familier with the transfer charactersitic of mosfets, this will be my first project so if you could explain to me in detail I would really apreciate it

Thanks in advance,

--Chris
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Old 10th October 2005, 07:23 PM   #8
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Quote:
Originally posted by DIY_newbie
Jneutron,

Thanks for looking at the DS!

These will be used in a class A audio amplifier so isn't it safe to assume the mosfet should always be on so the on/off rise time will not be detrimental?
For your app, the differences probably don't mean a hill of beans..

Quote:
Originally posted by DIY_newbie

Better thermal resistance =
I think the FC die is larger, so it is able to dissipate a little more heat..the difference also isn't that big.

Quote:
Originally posted by DIY_newbie

About the zero crossing, could you elaborate on what you wrote :

Transfer characteristics...IR has zero TC crossover at about 6.5 volts, FC is about 5.5 volts. Affects paralleling stability in linear or switching apps.

I'm not very familier with the transfer charactersitic of mosfets, this will be my first project so if you could explain to me in detail I would really apreciate it

Thanks in advance,

--Chris
If you look at the transfer graph for the FC device, there are 3 lines...-55, 25, and 150 C operation. If you put 4 volts on the gate of the device while it is at -55 C, it will carry about 100 milliamps. If you raise the temp to 25 C, it will carry 600 milliamps. At 150 C, it will carry 2.5 amps..At this gate voltage, the current will increase as the temperature increases...a positive temperature coefficient.

Now, if you put 5.5 volts on the gate, look at the curves..all three are at the same current...20 amperes..this means that at that gate voltage, the device current will be the same regardless of the temperature. This is a zero temperature coefficient.

Note that above 5.5 volts, the curves have crossed..increasing the temperature there means the devices will carry LESS current. This is a negative temperature coefficient.

If you parallel two devices, and both are on with gate less than 5.5 volts, if one device heats more than the other, it will conduct more current, this is a thermal runaway condition.

If you do the same, but they are above 5.5 volts, the hotter one will carry less current..this is more stable at that gate voltage.

It is easy enough to design the circuitry to get around this also..

For a simple on-off application with two devices, just make sure you run them with a gate voltage above the zero point in the curves. For the FC device, that is 5.5 volts, for the IR, 6.5.

For your app, source resistors most likely will suffice if you parallel them.

Cheers, John
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Old 10th October 2005, 07:38 PM   #9
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Remember too that you can hand identical devices to the
engineering and marketing departments of both companies
and still get different ratings.

My own experience with 240 types is that IR has a little better
matching in a lot, but I haven't noticed any other difference
worthy of comment. On the P channel devices, the Harris
wins by virtue of the more constant transconductance in the
mid-band audio frequencies.

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Old 10th October 2005, 09:00 PM   #10
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Looks like I'll be sticking with the real IR parts then, should make matching easier

Thanks for all the replies..

--Chris
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