abc_de
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Datasheet says 180mOhm.Rdson: .18mohm
Thus you should consider to use a suitable heatsink.Tj= Ta+Rth(j-a)XP
Tj= 40+62×8.82
Tj= 586.84
Not at all. There are plenty of heatsinks that can dissipate this heat in still air.Probably youll need a fan aswell....blowing over the heatsink.
That actually makes more sense. Spend your money on a better MOSFET rather than a large chunk of metalFor 7A and 0.18Ω Rds(on), the power dissipated is 49*0.18 = 8.8W which requires a heat-sink.
If you use a MOSFET with an Rds(on) of <20mΩ, which will dissipate <1W, then you shouldn't need a heat-sink.
Switching frq :2khzRemember switching losses too. What is switching frequency.?
It does seem very low power for an induction motor.
Is there current limiting anywhere?...if not, then maybe better use IGBTs
Usually induction motors are supplied straight off the mains....no drive transistors in there.
Drive transistors are usually a feature of BLDC's....or BLAC's.......or PMSMs
Due to cost reason i have only mosfet optionFor 7A and 0.18Ω Rds(on), the power dissipated is 49*0.18 = 8.8W which requires a heat-sink.
If you use a MOSFET with an Rds(on) of <20mΩ, which will dissipate <1W, then you shouldn't need a heat-sink.
Did you try an internet search? I bet there come a lot ofrather detailed documents.Can someone tell me Rth(j-c) : 1°c/w what it does mean.
1) You need to be concerned about more than Tc. The thermal resistance from case-to-ambient is the biggest contributor to your junction temperature rise. You're asking to keep Tc under 65 degrees. I don't know why you care at all about the case temperature, it's the junction temperature you need to be concerned about.Just want to know about TJ if Tc is known
1) You need to be concerned about more than Tc. The thermal resistance from case-to-ambient is the biggest contributor to your junction temperature rise. You're asking to keep Tc under 65 degrees. I don't know why you care at all about the case temperature, it's the junction temperature you need to be concerned about
Actually i am saying if current goes upto 7amp for short duration like 10usecNOW you start talking about a 10us pulse?I give up.
Actually i just consider the situation if current goes high for 10usecHi,
10us really is a completely new situation.
Thats my answer.10us of a IRF640, completely ON at 7A is no problem at all.
Maybe, maybe not.Thats my answer.
May be i could not put my question here proper way. Thats ture idealistic math and real circuit never same.Hi
Maybe, maybe not.
I guess - from reading your posts - that you are not aware that there is a discrepancy between this "idealistic mathematical" approch and the "real circuit" conditions.
You may simulate this idealistic scene without problems, but still in a real circuit your MOSFET may overheat.
Klaus
That’s already been answered.May be i could not put my question here proper way. Thats ture idealistic math and real circuit never same.
My problem was simple
Under id= 7amp (lets say now continuous load)
And room temperature 40 degree Celsius whats would be junction temperature and case temperature.
I do not know where i am not able to express
That’s already been answered.
You fail to say what the repetition rate of your 10 us pulse is. 20us?
In post #16 i said single pulse just for 10us no repetitive etc.
2 days?
I just post yesterday
That will determine your average current, and, thus, average power. As Klaus already told you, a single pulse will cause no perceptible temperature rise.
I know device can handle but i want to estimated mathematical value of Tj.
Can the device handle a single 7 amp pulse?
Irf640 can handle easily. That was not my purpose of post.
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