Guru
Joined: 09/08/2007
Location: AustraliaPosts: 4406
| Posted: 07:25pm 23 Oct 2018 |
Yup.
When you start to look at the de-rating curve and transient thermal impedance curve that huge "200 amps dc at 25C" rated device starts to shrink down into a midget.
All that many novices see at the top of the data sheet is that "200 amps maximum" and fail to realise that is just an unachievable theoretical maximum.
Somewhere to anchor one end of a sloping line that could otherwise just rise to infinity at some impossibly low sub freezing temperature.
Once you have defined that operating line between 25C and 160C, you can then pretty easily work out a reasonable safe operating current at any practical operating temperature somewhere in the middle.
That is the purpose. Nobody expects to work at either 25C or 160C they are the absolute unattainable limits. We are only interested in the region between.
You cannot run even at moderate power and hope to keep the little silicon thingy inside at 25C, even with chilled water cooling. But strangely its the 25 Celsius operating point that is used as the baseline temperature for the advertised maximum current rating. Its just the commonly accepted way of presenting the specification which is totally misleading to the uninitiated.
Those skinny mosfet legs are not going to be able to carry 200 continuous amps (laugh) and the whole idea of 200 amps continuous is ridiculous for either a TO220 or TO247 package.
Not only that, too many people think that the MAXIMUM rating limit line on the safe operating curve, just a whisker short of total destruction is a mighty fine place to plan on running that device.
But worst of all, those counterfeit Asian parts might never even come close to what a genuine part might be capable of doing. They could be perfectly o/k or maybe not.
Are you feeling lucky ?
Cheers, Tony.