
516
R
B
which is chosen to pass a reasonable current through it,
corresponds to the 'constant voltage' box in Fig. 27.7. The current to
be kept constant, passing through R
E
, provides the voltage
V
E
to
be
compared with V
z
. The difference between them is applied to TR.
Because of the high mutual conductance of the transistor chosen for
this role, a very small change in V
BE
, caused by any change in I
E
,
brings into play a very steep correcting action. Changes in load
resistance, R
L
, cause corresponding changes in V
EC
, but we know
(from Fig. 11.7, for instance) that this has very little effect on I
c
(and hence I
E
) and such effect as it has is correcte ...