Subject: Re: Confused in Massachussets, 2n7000 data sheet
Date: Sun, 05 Jan 2003 19:35:32 +0100
Organization: Wanadoo, l'internet avec France Telecom
NNTP-Posting-Date: 5 Jan 2003 18:35:39 GMT
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Winfield Hill wrote:
> 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
> operation. Interesting.
May it be that the Delta-V is with respect to the (variable) gate threshold
voltage needed to get 1mA - for each given temperature ? That threshold
voltage decreases with temperature (ref. the Normalized Gate-Source voltage
versus temperature graph, earlier in the datasheet (I am looking at a
DS from Vishay))...
> - Win