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CIRCUIT
NSA
SsSA-8800
POWER
STAGE
RL
Fig. 5-4
Power Limiter Circuit
Fig. 5-5
Bridge Circuit
NSA (Non-Switching Amplifier) Circuit
By operating
the power stage only within the
active region (no possible cut-off) and with mini-
mum
idle current,
the NSA
circuit prevents the
generation
of switching
distortion
and
reduces
heat loss.
Operating Principle
Since idle current flows through normal class B
SEPP
power stages (see Fig. 5-6) when no signal
' is applied, the DC level is shifted by D and VR by
a fixed amount
(with the voltage across points P
and R serving as a bias). The voltages across points
P and Q, and Q and R at this time will be equal.
When the positive portion of a signal is applied to
this circuit, the power stage current on the NPN
side
is increased
resulting
in the voltage
across
points
P and
Q also
being increased.
However,
since the voltage across points P and R is practi-
cally constant (see note), the voltage across points
P and R (PNP power stage bias) will be decreased,
resulting in the PNP power stage being cut off.
O
PRE-DRIVER
~vcc
Fig. 5-6
Normal Power Stage
11
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