Page 31
Com-Tech Power Amplifiers
Reference Manual
The protection mechanisms that affect the signal path
are implemented to protect the amplifier under real-
world conditions. These conditions are high instanta-
neous current, excessive temperature, and output
device operation outside safe conditions.
Two transistors act as a conventional current limiter,
sensing current in the output stage. If current exceeds
safe levels, the limiters remove the drive from the LVAs,
limiting current in the output stage to a safe level.
To further protect the output stages, the patented ODEP
circuitry is used. It produces an analog output propor-
tional to the always changing
safe operating area of the
output transistor. This output controls the translator
stage previously mentioned, removing any further drive
that may exceed the
safe operating area of the output
stage.
A thermal sensor supplies the ODEP circuits with infor-
mation on the operating temperature of the heat sink on
which the output devices are mounted.
Should the amplifier fail in a way that would cause DC
across the output lead, the DC protection circuit senses
this on the negative feedback loop and shuts down the
output stages until the DC is removed.
5.2.2 Bridge-Mono Operation
By setting the dual/mono switch on the back panel to
Bridge-Mono, the user can convert the Com-Tech into a
bridge-mono amplifier. With a signal applied to the
Channel 1 input jack, and the load between the positive
(+) output terminals on the back panel, twice the volt-
age can be output.
The Channel 1 output feeds the Channel 2 error amp.
Because there is a net inversion, the Channel 2 output is
out of polarity with Channel 1. This produces twice as
much voltage across the load. Each of the channel’s
protection mechanisms work independently if a fault
occurs.
5.2.3 Parallel-Mono Operation
With the dual/mono switch set to Parallel-Mono, the out-
put of Channel 2 is paralleled with the output of Chan-
nel 1. A suitable high current-handling jumper must be
connected across the positive (+) output terminals to
gain the benefits of this operating mode.
The signal path for Channel 1 is the same as previously
discussed, except that Channel 1 also drives the out-
put stage of Channel 2. The Channel 2 balanced input,
error amp, translators and LVAs are disconnected and
no longer control the Channel 2 output stage. The Chan-
nel 2 output stage and protection mechanisms are also
coupled through S1 and function as one.*
In Parallel-Mono mode, twice the current of a single
channel is available. Because the Channel 2 ODEP cir-
cuit is coupled to Channel 1, you have added protec-
tion if a fault occurs in the Channel 2 output stage. The
Channel 2 ODEP circuit limits the output of both output
stages by removing the drive from the Channel 1 trans-
lator stages.
_______________________
* Note: When the amplifier’s dual/mono switch is moved to the Parallel/
Mono position, the Channel 2 IOC indicator will illuminate. This is a nor-
mal condition in this configuration.
