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The Class-I Amplifier
Crown Audio, Inc.
P.O. Box 1000
Elkhart, IN 46515-1000
TEL: 219-294-8200
FAX: 219-294-8FAX
www.crownaudio.com
Trademark Notice:
Crown
®
and
BCA
®
are registered trademarks of Crown International.
Printed in U.S.A.
137234-1
12/03
amount. Class-I uses symmetrical interleaved PWM,
meaning both the leading edges and trailing edges of
the pulse are varied according to the amplitude of the
signal, and the spacing between pulse centers remains
constant. Both the positive and negative switch pulses
remain aligned on-center, and the net output current is
positive.
Class-I Switches, Positive Signal
Class-I Switches, Negative Signal
Reactive Energy Returned to Amplifier
From Loudspeaker
Likewise, to produce a negative output signal, the
output of the negative switching device is increased in
duty while the positive switching device is decreased by
the same amount. Again, both switch pulses remain
aligned on-center, and the net output current is negative.
tive energy returned from the loudspeaker to the ampli-
fier is reabsorbed and output again to the loudspeaker
with little loss. Non-switching, dissipative amplifiers are
forced to dissipate all of the returned energy and more
in the form of heat. This means class-I amplifiers are
louder than other amplifiers with comparible power
specs, yet they stay much cooler, and can be lighter
since they don’t need nearly as much mass for heat
dissipation.
Dissipative Amplifier
Class-I Amplifier
Reactive Energy
Reactive Energy
The result of using interleaved PWM is that by operating
the switching devices at 250 kHz, the signal is effectively
modulated at 500 kHz since both the leading and trailing
edges of each pulse contribute to the output ripple
current. This arrangement further increases efficiency,
since switching losses are effectively halved by operat-
ing the switching devices at 250 kHz, rather than at 500
kHz as would be necessary with class-D designs to
achieve the same effective sampling of the waveform.
Class-I amplifiers also have all of the nearly ideal power
converter attributes of class-D PWM amplifiers, in that
reactive loudspeaker loads are easily driven. The reac-
With it’s rock-solid reliability, high quality audio repro-
duction and unmatched efficiency, Crown’s patented
class-I technology creates a totally new paradigm for
amplifier design that represents the future of profes-
sional amplifiers.