(a) Control Settings
(b) Result
Figure 13: 2N4401 NPN BJT
The move the cursor into the curve area and the cursor display then shows the voltage and current at the cursor
position.
3.13
Lambda Diode, Negative Resistance Device
The
lambda diode
is a circuit that behaves as a negative resistance over part of its VI characteristic. The circuit
and characteristic are shown on pages 18 and 19.
From the literature
3
, we expect the shape of the curve to have a peak, followed by a valley, followed by a
rising portion. Should we test this using a current source or voltage source?
A current source creates a load line that is horizontal, so varying the test current causes this horizontal line to
change it’s vertical position. This load line can intersect with the VI characteristic simultaneously at as many as
three points, which leads to an ambiguous result.
A voltage source creates a load line that is vertical and changes its horizontal position. This load line can
intersect with the VI characteristic at one point only, so the result is unambiguous.
Consequently, the device should be driven by a constant voltage source, while measuring the current. In the
CTR-201, that implies connecting it between the collector (Red) and emitter (Black) terminals, which are both
voltage sources. The current drive (Blue) terminal is not used.
This is similar to the test method for an NPN BJT and N-Channel MOSFET, where the characteristic is tested
by applying a voltage and measuring the current.
3.14
Vacuum Tube
Figure 19 on page 19 shows the it plate characteristic of a low-voltage vacuum tube, Russian type 1zh18b. The
vacuum tube operates in a similar manner to an N-Channel JFET, and so the JFET setting was used on the curve
tracer. An external power supply of 1.2 volts was also required to power the filament in the tube.
3
Lambda Diode
and
negative resistance
.
15
