Features:
The Robust Amplifier is a combination of a current limited power supply
with a high current low impedance power output stage. Any short
circuit on the output is instantly current limited. The output
stage utilizes two high current transistors with no emitter
resistors. The two high current output transistors are uniquely
biased off of emitter resistors of two additional high current gain
transistors. The amplifier was designed so that all three
transistor associated with the power for each (+ and -) power supply
rail can be mounted to the same heat sink without the need for
electrical isolation. The use of old CPU heat sinks works
well. Being that there is metal to metal contact between the
transistors and heat sinks, the amplifier can be biased hot to
eliminate crossover distortion. This amp also features adjustable
output stage bias. The schematic shows +- 45 volts power supply,
this is a maximum, 35v is recommended.
ROBUST AMPLIFIER SCHEMATIC
The power is supplied by a split power supply circuit with an
instant current limit built in. This current limited supply
protects the amplifier's output transistors from output shorts and
current surges during power on. This design utlities scable
current sensing resistors. You can choose the current limit that
is right for you output transistors.
7 Amp limit use 0.1 ohm
10 Amp limit use 0.068 ohm
Current limit circuit operation is as
follows.
Current flow throug R17 creates a voltage, when this voltage reaches
0.7v Q12 turns on and turns off Q10. When Q10 is off voltage
develops across Q10 and this voltage is used to drive the OL (overload)
LED1.
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