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From: Robert Strand
Subject: Re: Confused in Massachussets, 2n7000 data sheet
Date: Thu, 09 Jan 2003 09:52:01 +1100
Organization: ihug ( New Zealand )
References: <3E1A6858.email@example.com> <3E1B264A.1430F6FC@worldonline.fr>
NNTP-Posting-Date: Wed, 8 Jan 2003 22:54:38 +0000 (UTC)
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> I believe you meant TA, correct? Since V_(GS)(TA) has a negative tempco,
> V_(GS)(TA)+deltaV_0 decreases with TA and can compensate (over large delta TA)
> the positive tempco of I_ds at a fixed V_GS, for some delta V_0 such that
> V(GS)(25°C)+delta V_0 is below the 3.7-4.3 v threshold (which one can see,
> e.g. on the OnSemi's datasheet). If V_GS(TO) was for 25C then
> V_GS(TO)+delta_V would be a fixed voltage, and we won't get zero tempco for
> delta_V below 1.5V.
> So "TO" is probably a typo for "TA". I wonder however about the utility of
> this graph compared to the
> graph of the family of the transfer characteristics at different temperatures.
I did mean 25C. I actually interpreted V_GS(TO) to be V_GS(TH) at 1mA 25C,
this also agreed with the V_GS(TH) in the tabulated data. I would have
thought if V_GS(TO) (whatever it is) was defined at TA (ie. variable temp)
then the constant deltaV would effectively track the device V_GS(TH)
variations with temperature and hence removed their effect- if that was the
case I'd expect to see only positive Rds_on tempco effects due to the
device's beta parameter.
I'll have to read the data sheet again and see if it's possible to get a
-ve tc with the contraint of Ids = constant with variable Ta.
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