Crown Micro-Tech 1201 Informations techniques télécharger pdf (Page 24)

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Micro-Tech 600/1200/2400 Power Amplifiers

Reference Manual

with their push-pull effect through the bias servo Q318,

drive the fully complementary output stage.

The bias servo Q318 is thermally coupled to the heat

sink and sets the quiescent bias current in the output

stage to lower the distortion in the crossover region of

the output signal. D301, D302, D303, and D304 remove

the charge on the unused portion of the output stage

based on the polarity of the output signal.

With the voltage swing provided by the LVAs, the signal

then gains current amplification through the Darlington

emitter-follower output stage.

The bridge-balanced circuit (U104-D) receives a signal

from the output of the amplifier and compares it to the

signal at the Vcc supply. The bridge-balanced circuit

then develops a voltage to drive the bridge-balanced

output stage. This results in the Vcc supply

having exactly one half of the output voltage added to

their quiescent voltage. D309, D310, D311 and a trim-

mer resistor set the quiescent current point for the

bridge-balanced output stage.

The protection mechanisms that affect the signal path

are implemented to protect the amplifier under real-world

conditions. These conditions are high instantaneous cur-

rent, excessive temperature, and output device opera-

tion outside safe conditions.

Q107 and Q108 sense output current and act as a com-

mon current limiter. When instantaneous current exceeds

the design criteria, the limiters remove the drive from

the LVAs to limit output current to safe levels.

To further protect the output stages, the patented

ODEP

circuitry is used. It produces an analog output propor-

tional to the always changing die temperature of the out-

put transistor. This output controls the translator stage

previously mentioned, removing any further drive that

may exceed the

safe operating area

of the output stage.

Thermal sensors S100 and S200 give the

ODEP

circuits

vital information 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 stage drive until the DC is removed.

5.2.2 Bridge-Mono Operation

By setting the back panel stereo/mono switch to Bridge-

Mono, you can convert a

Micro-Tech

amplifier for

bridged-mono operation. With a signal applied to the

channel 1 input and the load connected between the

positive (+) output terminals, twice the voltage can be

delivered to the load.

The channel 1 output feeds the channel 2 error amp

U204-A. The signal feeding channel 2 is inverted so the

channel 2 output will have the opposite polarity of chan-

nel 1. This makes it possible to deliver twice as much

voltage to the load while the protection mechanisms for

each channel continue to work independently.

5.2.3 Parallel-Mono Operation

With the stereo/mono switch set to Parallel-Mono, the

output of channel 2 is paralleled with that of channel 1.

A suitable jumper capable of handling high current 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 output

stage of channel 2. The balanced input, error amp, trans-

lators, and LVAs of channel 2 are disconnected and no

longer control the channel 2 output stage. The channel

2 output stage and protection mechanisms are also

coupled through S1 and function as one.

In Parallel-Mono mode, the amplifier can deliver twice

the current of a single channel. Because the channel 2

ODEP

circuit is coupled through S1, the amplifier gains

additional protection if a fault occurs in the channel 2

output stage. The channel 2

ODEP

circuit will limit the

output of both output stages by removing the drive from

the channel 1 voltage translator.

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Crown Micro-Tech 1201 Informations techniques Page 24

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