Ecler DT4800, Руководство по обслуживанию

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52-0024-0100 EP05-02 Mòdul (Anglès).doc 3 of 4
OUTPUT FILTERS AND DC-PROTECTION.
The output filters, together with the DC-Out protection circuitry, are made of this
elements:
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A Differential mode filter.
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A Common mode filter.
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An EMI enhancement filter.
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A Zobel network-type compensating circuitry.
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The DC-Out protection circuitry.
The Differential mode-configured filter is used to clean high-frequency voltage from
the output signal. It is made of two capacitors and two induction coils. Such a filter is
placed on each of the half-bridge branches connected to the loudspeakers. Using this
filters, the 250KHz carrier signal is rejected, and only clear audio signal reaches the
loudspeakers.
The common mode-configured filter is also made of a capacitor and an inductor, and
is used to eliminate the carrier wave leakages from each output, as this noise signal has
the same polarity on each half-bridge output when referred to signal ground (0V).
The EMI-enhancement filter is placed nearby the final Speakon-type output
connection. This has to be done in order to avoid any kind of RF signal generated inside
the unit to be radiated into the environment.
The DC-Out protection circuitry is the same as the used in our analogue power
amplifiers. In case this circuit detects DC-levels, or very low frequencies (below 10Hz) with
more than 30V amplitude between the unit’s OUT+ and OUT- outputs, a TRIAC shorts the
output poles, avoiding the loudspeakers from being damaged by DC-signals.
FEEDBACK.
In order to ensure the stability of this modules, the correct feedback type has to be
chosen. When referring to PWM amplifiers, this feedback networks are more critical than
those used in analogue amplifiers. In our case, a double feedback system is being used:
sampling the amplifier’s output voltage after filtering, and the current flowing through one
of the differential filter coils.
The improvement obtained by using this second type of current-based feedback loop
consists in the possibility to reduce the output’s LC filter from a second to a first order
type of filter.