Replacement For Toshiba 2SK170/2SJ74
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diyAudio Member

Join Date: Aug 2006
Quote:
 Originally Posted by scott wurcer That's a relatively poor measure of Vp because the FET is in the subthreshold region. It is better to measure Vgs at two currents one above subthreshold like 200uA and one below Idss and use the FET equations given for Id vs Vgs. Two measurements two equations and solve for Vp and Idss.
Hi Scott,

I was puzzled with Vp of few samples of j74bl which I have.

They track prety well at working currents but Vp at 0.1uA is about 100mV different.

sample1: Idss-6.73mA, Vp @ 0.1uA -510mV, gm@5.5mA -34.31mS
sample2: Idss-6.76mA, Vp @ 0.1uA -618mV, gm@5.5mA -34.93mS

Is it about what you talked?

scott wurcer
diyAudio Member

Join Date: Jan 2004
Location: Belmont MA
Quote:
 Originally Posted by radule Hi Scott, I was puzzled with Vp of few samples of j74bl which I have. They track prety well at working currents but Vp at 0.1uA is about 100mV different. sample1: Idss-6.73mA, Vp @ 0.1uA -510mV, gm@5.5mA -34.31mS sample2: Idss-6.76mA, Vp @ 0.1uA -618mV, gm@5.5mA -34.93mS Is it about what you talked?
In general yes, the deviation from square law behavior starts well before 0.1uA in my plots (which I lost in a drive crash).
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