Electronics > Electronics

IRFP-450 Mos Fet Harris

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Militoy:
The higher voltage parts will work OK. You will just (generally) get lower forward voltage drop from a lower voltage transistor. You wouldn't want to use a 500V FET at 500 Volts, anyway. You need to leave a little headroom as a safety factor from switching voltage spikes, input voltage variation, etc. I usually try to select a transistor rated for around twice the voltage I will be using it at (same goes for caps).

Admin:

--- Quote ---I usually try to select a transistor rated for around twice the voltage I will be using it at (same goes for caps).
--- End quote ---
I completely agree. Ive seen too many caps explode from people who forget this . . . reversing a motor already at full forward speed would cause the spike . . .

You might also want to consider using a mosfet driver to boost efficiency. The one I use is IXDD404PI made by IXYS. Its listed as '4 Amp Dual Low-Side Ultrafast MOSFET Driver.'

The higher the mosfet gate voltage, the higher the efficiency (reduced heat output, too). This is the advantage of using the driver.

ps -
Not sure how reliable this chip is (or if I just didnt account for something in my circuit) . . . I used it for like 4 months with no problem . . . then the day a representive from ONR came by to see my prototype it went up in smoke for no reason . . . blast you, murphy and your law!

Cognaut:
It sounds like another case of "tin whiskers."   ;D 

Admin:
interesting . . . never heard of it before . . .
http://en.wikipedia.org/wiki/Whisker_(metallurgy)

im sure the fact that my circuit board was never more than 2 feet away from a large fish tank for all those months had something to do with it . . .  :P
(the curse of aquatic robotics)

Militoy:
ICs and hybrid modules have become more and more reliable in recent years – and a catastrophic failure is now usually the result of the designer or user exceeding some Absolute Maximum Rating parameter of the part that failed – as opposed to “Infant Mortality”. ESD over-voltage damage from improper handling is a common culprit, as are un-planned-for voltage transients, over-temperature, or just plain making mistakes in the design application. There are no mysteries in electronics design – sometimes though, you just haven’t gathered enough data to understand a situation.

Re: tin Whiskering – The growth of tin sulfide whiskers on tinned component leads, and their effect on the solderability of the affected parts has been a major problem in military electronics for years. The problem results from the use of pure tin to plate solderable leads. When placed in proximity with a cardboard box or paper which is processed with acid, the outgassing of sulfur dioxide from the paper causes the growth of tin sulfide crystals, or “whiskers” on the plated surfaces. Soldering of the leads is then difficult or impossible, and failure of the soldered joint is not unusual. Most defense contractors have requirements in their specifications that the tin plating on component leads contain at least 3% lead in the alloy, in order to prevent whiskering. The problem becomes very tricky, as European ROHS standards prohibit the use of lead on component leads – so all the parts manufacturers are omitting lead from their plating process.

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