Application Examples
5
Keysight U1401B User’s and Service Guide
117
You can identify the channel type of a JFET by measuring its drain-source
resistance (R
DS
) when it is biased with a constant voltage source. Usually, both
channel types will switch on under a gate-source voltage (V
GS
) of 0 V.
5
Connect the red input probe lead to the drain.
6
Connect the black input probe lead to the source.
7
Connect the red output alligator lead to the gate terminal through a 100 k
Ω
resistor, and connect the black output alligator lead to the black input probe
lead.
If R
DS
increases when V
GS
is a negative value, then it is an n-channel JFET. On the
other hand, if R
DS
increases when V
GS
is a positive value, then it is a p-channel
JFET.
Table 5-7
Gate terminal according to probe test
Pins
Test leads
Gate
Red/Black
Black/Red
1-2
<
1 k
Ω
<
1 k
Ω
3
1-3
<
1 k
Ω
<
1 k
Ω
2
2-3
<
1 k
Ω
<
1 k
Ω
1