2-17
Switching Diode Test
To effectively test diodes used for computer applications, you must obtain back-resistance
measurements at a large number of different voltage levels. This can be done efficiently by using a
dynamic diode tester in conjunction with an oscilloscope, which is used to display the diode’s back-
current-versus-voltage curve. You can easily interpret diode characteristics, such as flutter, hysteresis, and
negative resistance, through use of the dynamic current and voltage display.
DIODE CHARACTERISTIC GRAPHICAL DISPLAY
You can use an oscilloscope to graphically display the forward- and back-resistance characteristics
of a diode. A test circuit used in conjunction with an oscilloscope is shown in figure 2-7. This circuit uses
an audio-signal generator as the test signal. It should be adjusted for an approximate 2-volt, 60-hertz
signal, as measured across R1.
Figure 2-7.—Display circuit used with an oscilloscope.
The test signal you apply to the diode is also connected to the horizontal input of the oscilloscope.
The horizontal sweep will then display the voltage applied to the diode under test. The voltage developed
across current-measuring resistor R2 is applied to the vertical input of the oscilloscope. Since this voltage
is proportional to the current through the diode under test, the vertical deflection will indicate diode
current. The resulting oscilloscope trace will be similar to the curve shown in figure 2-8.
