From: Winfield Hill
Subject: Confused in Massachussets, 2n7000 data sheet
Date: 5 Jan 2003 09:00:20 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.20
Whew, my poor brain must be showing its age.
Something simple in General Semiconductor's old 2n7000 data sheet has
me confused (it's missing from the newer Siliconix / Temec data sheets,
but I can send a pdf file of the old data sheet to anyone who'd like).
Page 4 has a graph, Normalized Drain Source Resistance vs Temperature.
The x-axis is temperature and y-axis shows r_DSn = r_DS(Ta)/r_DS(25C),
the ratio of Rds(T) to Rds at 25C, which is fine. We see four plots,
labeled delta-V 0.5V, 1V, 2V and 3V, where delta-V = V_GS - V_GS(To),
and also V_GS(To) at I_D = 1mA. Whew, what's that about? Are they
showing the variation of R_ds(on) with temperature for four different
gate voltages, above some (linear operation) gate-voltage threshold?
I.e., if it takes Vgs = 2.0V to get 1mA linear conduction, then are
these Rds(on) plots for Vgs = 2.5, 3.0, 4.0 and 5.0 volts? Page 5 has
an Rds(on) vs. Vgs plot; here Rds plots to about 13, 8.5, 6 and 5 ohms
respectively. The page 4 plot shows a strong negative Rds tempco for
the Vgs = 2.5V, Rds = 13-ohm case, and a near zero tempco around 25C
for the 3V, 8.5 ohms case, then shows the familiar strongly-positive
Rds tempcos for the higher gate voltages. This can be compared with
the Id vs. Vgs transfer-function plots in other manufacturer's 2n7000
data sheets, where the -55, 25 and 125C temperature plots cross at
about Vgs = 3.7 to 4.3V, showing the zero-tempco region for linear