
217
ΙΟΒΌΛΕ
+ 0· It is therefore many times larger than
I
CBO
.
Note the
capital letter subscripts in h
FE
, signifying that it is the d.c. no-signal
ratio
I
C
/IBI
not
the signal ratio
i
c
/i
b
as in the last chapter. h
FE
and hf
e
are usually of the same order, at least; but both depend somewhat on
the working point and temperature.
/ CBO
(a) (b) (c)
Fig. 13.3 For the elucidation of leakage currents in transistors
A typical value of
I
CBO
for a low-power germanium transistor at
25° C is 3 μΑ.
I
CEO
could therefore be something like 200 μΑ, or
0.2 mA. As the leakage doubles for about every 9° C, at 70° C this
would have risen to almost 6 mA. In a case suc ...