Re: "transconductance may limit current"

From: John Popelish (jpopelish_at_rica.net)
Date: 01/23/05 

Date: Sat, 22 Jan 2005 22:41:17 -0500

kellrobinson@yahoo.com wrote:
>
> If I want this mosfet to conduct several hundred amps by shorting a car
> battery briefly, what is the meaning of the note about transconductance
> on fig 5, Peak Current Capability and how do I know whether that's an
> issue in this application?
> http://www.fairchildsemi.com/ds/RF/RFP30N06LE.pdf

>From figure 4, it looks like you may be able to conduct about 100
amperes for as long as 100 us if the battery holds up to 10 volts
under that load. The triangular area below 100 amperes and down to
zero volts across the transistor is probably not possible to achieve
because of the channel resistance. I am very doubtful if you can get
hundreds of amperes through this device with even a full 12 volts at
the battery, because of the current limit effect that rounds off the
current for the top curve on figure 7. You will also need a gate
drive voltage that is not the battery under load. 

-- 
John Popelish

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