AN4853 Application Note
AN4853
Thyristor / Diode Measurement With A Multimeter
Application Note
Replaces September 2000 version, AN4853-3.0
AN4853-3.1 July 2002
Many users of thyristors and diodes lack the proper equipment
to make measurements of semiconductor parameters. The
readily available battery operated multimeter is often used to try
to determine the difference between acceptable and non-
acceptable devices using a resistance reading. A reading of this
type can lead to incorrect conclusions.
curve. The blocking voltage of a thyristor is defined as the
voltage at which it reaches a specified leakage current at the
defined temperature. Therefore devices can have a variety of
leakage current characteristics and still be within specification.
PRECAUTIONS
MULTIMETER MEASUREMENTS
The multimeter is generally used to measure the DC resistance
between anode and cathode of thyristors and diodes and also
the gate to cathode on thyristors. These measurements are of
the “off state” or blocking voltage of the device.
The only valid readings are “open circuit” and “short circuit”. The
anode to cathode or gate to cathode measurement must register
a short circuit in both directions ( forward and reverse polarity) for
the device to be declared short and infinite resistance for an open
circuit.
The measurement of resistance with a multimeter is an
inappropriate measurement technique for separating good
devices from bad. When a resistance measurement is taken with
an multimeter, the internal battery voltage is typically in the range
1.5V to 15V and the leakage current of the device at this voltage
will determine the measured resistance. A semiconductor has a
non-linear blocking voltage/leakage current characteristic and
hence a non-linear resistance
1. Ensure that the resistance reading is only being taken across
the device and not across something in parallel with it.
2. If a disc type device is being measured, make sure that
it is under sufficient load to ensure that the internal components
are pressed together and high resistance readings are
avoided.
SUMMARY
A multimeter resistance measurement is not recommended for
determining acceptable semiconductor devices. As a quick
check for devices in a circuit, a multimeter will allow you to
determine if a device has failed catastrophically. The device with
the lowest leakage current at 3V is not necessarily the one with
the lowest leakage current a high voltage.
Leakage current - (mA)
Leakage current limit
1
0.01
0.001
3kΩ
300kΩ
3MΩ
3V
Blocking voltage - (V)
Voltage grade
Fig.1
1/2
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