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SECTION 4
THEORY OF OPERATION
4.1 General Information
The Micro-Tech amplifier incorporates several new
technological a d v a n c e m e n t s including real-time
computer simulation, a low-stress output stage, and an
advanced heat-sink embodiment.
The Micro-Tech has extra circuitry to limit current and
temperature to safe levels, making it highly reliable
and tolerant of faults. Unlike many lesser amplifiers, it
can operate at its voltage and current limits without
self-destructing.
Real-time computer simulation is used to create an
analog of the output devices' junction temperature,
which is unmeasureable directly. Current is limited
£ only when the device temperature becomes excessive
- and just by the minimum amount necessary. This
patented approach maximizes the available output
power and eliminates overheating - the major cause of
device failure.
The topology used in the Micro-Tech amplifier output
stage is called "the full bridge," and makes full use of
the power supply. This patented topology also provides
peak-to-peak voltages available to the load that are
twice the voltage the output devices are exposed to.
T h e f u l l - b r i d g e topology is g r o u n d - r e f e r e n c e d .
Composite devices are constructed to function a s
gigantic NPN and PNP devices, since the available
currents exceed the limits of available devices. Each
output stage has two of these composite NPN devices
and two composite PNP devices.
The devices connected to the load are referred to a s
"high-side NPN and PNP' and the devices connected
to ground are referred to as "low-side NPN and PNP."
Positive current is delivered to the load by increasing
conductance simultaneously in the high-side NPN and
low-side PNP stage, while decreasing conductance of
the high-side PNP and low-side NPN in synchrony.
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The two channels may be used together to double the
voltage or the current presented to the load. This
feature gives the user flexibility in maximizing the
power available to the load.
The Micro-Tech amplifier utilizes a wide-bandwidth
m u l t i - l o o p d e s i g n t h a t u s e s s t a t e - o f - t h e - a r t
c o m p e n s a t i o n t e c h n i q u e s . T h i s p r o d u c e s i d e a l
behavior and results in ultra-low distortion values.
Aluminum extrusions have been widely used for heat
sinks in power amplifiers due to their low cost and
reasonable performance. However, measured on a
watts/pound b a s i s or a w a t t s / v o l u m e b a s i s , the
extrusion technology doesn't perform nearly a s well a s
the heat-sink technology developed for the Micro-Tech
power amplifier.
The Micro-Tech heat sinks are fabricated from custom
convoluted fin stock that provides an extremely high
ratio of area to volume, or area to weight. All power
d e v i c e s a r e m o u n t e d d i r e c t l y to m a s s i v e h e a t
spreaders that are electrically hot. Making the heat
spreaders electrically hot allows improved thermal
performance by eliminating the insulating interface
underneath the power devices. The chassis itself is
used as part of the thermal circuit, and this maximizes
utilization of the available resources.
4.2 Block Diagram Circuit Theory
STEREO OPERATION
For simplicity, the discussion of stereo operation will
refer to one channel only. Mono operations will be
discussed later.
Please refer to the block diagram (Fig. 4.1) and the
schematic.
The signal at the input jack passes into the balanced
gain stage ( U 1 0 4 - C , D ) where b a l a n c e d - t o - s i n g l e -
ended conversion t a k e s place using a d i f f e r e n c e
amplifier. From there, gain can be controlled with a
potentiometer. The error amp (U104-A) amplifies the
difference between the output signal and the input
signal from the gain pot, and drives the voltage-
translator stage.
The voltage-translator stage channels the signal to the
Last Voltage Amplifiers (LVA) depending on the signal
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