Specifications
CONSTRUCTION
Fig. 1: Schematic circuit diagram of the transistor lead identifier
tions. As a result, the
LED
s con-
nected to the collector and emit-
ter leads start flickering alter-
nately with different bright-
ness. By inserting a resistor in
series with the base, the
LED
glowing with lower brightness
can be extinguished.
In the case of an
NPN
de-
vice (under normal biasing
condition), conventional cur-
rent flows from source to the
collector layer. Hence, the
LED
connected to the collector only
would flicker brighter, if a
proper resistor is inserted in
series with the base. On the
other hand, in case of a pnp
device (under normal biasing
condition), current flows from
source to the emitter layer. So,
only the
LED
connected to the
emitter lead would glow
brighter. As the type of device
is already known by the base-
Id logic, the collector lead can
be easily identified. Thus, for
a particular base-Id, position
of the collector would be indi-
cated by one of the two num-
bers (we may call it collector-
Id) as shown in column 7 of
Table I.
Error processing. Dur-
ing collector identification for
a pnp- or an npn-device, if the
junction voltage drop is low
(viz, for germanium transis-
tors), one of the two currents
in the
C
-
E
path (explained
above) cannot be reduced ad-
equately and hence, the data
may contain two logic-1s. On
the other hand, if the device
beta is too low (viz, for power
transistors), no appreciable
current flows in the
C
-
E
path,
and so the data may not con-
tain any logic-1. In both the
cases, lead configuration can-
not be established. The rem-
edy is to adjust the value of
the resistor in series with the
base. There are three resistors
(10k, 47k, and 100k) to choose
from. These resistors are con-
nected in series with the test-
ing terminals 1, 2, and 3 re-
spectively. The user has to ro-
tate the transistor, orienting
7