Peak Atlas DCA75 Pro, Руководство пользователя

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Peak Atlas DCA Pro User Guide June 2019 – Rev 1.7
Page 27
“ On ” Characteristics
The
DCA Pro
measures the gate-source
voltage required to reach the onset of
good conduction through the JFET
’
s
drain-source. Good conduction is determined when the drain-source current
reaches 5mA. For JFETs that have a lower saturation current (I
DSS
) than 5mA,
the DCA Pro will select a lower “ on ” current.
Transconductance
While the JFET is conducting, the
JFET
’
s gain (transconductance) is
measured. Transconductance is often
measured in mA/V, mmhos or mSiemens. This refers to the change in drain
current resulting from a change in gate-source voltage:
g
fs
= Δ I
DS
/ Δ V
GS
The
DCA Pro
measures transconductance by determining the gate voltage
change necessary to obtain a drain current change from 3.0mA to 5.0mA. If the
JFETs saturation current (I
DSS
) is less than 5.0mA then a proportionately lower
current span will be used.
I
DSS
Drain Current (for V
GS
=0)
Finally, the drain current for a zero
gate-source voltage is measured. This is
measured for a drain-source voltage of nominally 3.0V but may be lower if the
drain current exceeds 12mA.
Transconductance is measured by the DCA Pro over a small range of
drain current (typically a span of 3-5mA). Values of transconductance
higher than 20mA/V can yield a coarse measurement resolution as the
required change in gate voltage is so tiny. Values above 99mA/V are
displayed as
“
>99mA/V
”
.