PLM Series Operation Manual
19
OPERATION AND PERFORMANCE 7
Power ratings are based on a “real-life” duty cycle of
25 ms full power every 400 ms. Between bursts, a
lower signal level applies, such that the continuous
average power is 1/8th of the rated power.
In reality, when some channels are delivering less than
maximum rated power, energy reserves in the PSU
are available to permit other channels to deliver more
power. The graph shows the peak output voltage over
time for a continuous sine wave is applied.
If all four channels are driven with the same signal
into the same impedance (solid red line), then the rail
voltage (dotted red line) will drop faster than when two
channels are delivering “max power” (solid blue line)
and two channels are delivering “half power” (solid
orange line). This is termed asymmetric loading. The
rail voltage for this is the dotted blue line.
It can be seen that higher power output is available for
25 ms bursts with asymmetric loading.
7.3 Amplifier and Load
Protection systems
The PLM is equipped with a comprehensive set of
protection circuits. If operating conditions become
sufficiently extreme that any of these circuits become
active, indication is provided by LEDs in one or more
soft buttons 5-8, together with adjacent warning text.
In addition to this, notification is also presented within
the Dolby Lake Controller PLM Edition software and
within system log files.
7.3.1 Inter-sample Voltage Peak Limiter
(IsVPL)
The ISVPL is a high quality voltage limiter. Its purpose is
to ensure that the voltage at the output terminals never
exceeds the threshold which has been set. It operates
on two fundamental principles:
The signal is delayed slightly in order to allow
▸
the ISVPL to “look ahead” and reduce the gain
before any voltage in excess of the threshold can
appear at the output. This results in zero voltage
overshoot at the output.
The amplitude of the output signal “between”
▸
digital samples is predicted. This permits the
ISVPL to respond to analog peaks that may occur
at the power output.
The table below represents the absolute maximum
output power that an individual PLM channel can
deliver at the given ISVPL setting and impedance
shown.
The formula for generating the value for a
desired power into a load is
V
peak
=
Z
P
2
The formula for calculating the power
for a given ISVPL setting is
P
=
Z
V
peak
2
2
where |Z| is the magnitude of the complex load
impedance in ohms.
Table 7-3
* Note that these ratings are limited by the CPL (Current
Peak Limiter) functions, not by ISVPL settings, due to
amplifier channel current capacity
The ISVPL threshold may be set at any level between
17.8 V and 153 V (model dependent) via the PLM’s
menu system. (See Section 9.12.2.5.1 or the Dolby
Lake Controller User Manual PLM Edition Addendum
MAX. sINEWAVE bURsT POWER (Watts)
Load Impedance
(ohms)
2.7
4
8
16
IsVPL sETTING
(V
peak
)
153 (max.)
3365*
2926
1463
732
150
3365*
2813
1406
703
121
2742
1830
915
458
101
1910
1275
638
319
83
1290
861
431
215
70
918
613
306
153
56
587
392
196
98
47
414
276
138
69
38
361
181
90
45
17.8 (min.)
79
40
20
10
