Amplifier And Load Protection Systems; Inter-Sample Voltage Peak Limiter (Isvpl) - Lab.gruppen PLM Series Operation Manual

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 function 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
OPERATION AND PERFORMANCE 7
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.
An ISVPL-to-load calculator that will assist in
generating the appropriate ISVPL setting for
a desired power load isavailable at www.
labgruppen.com/plm
MAX. sINEWAVE bURsT POWER (Watts)
Load Impedance
2.7
(ohms)
IsVPL sETTING
(V peak)
153 (max.) 3365*
150 3365*
121 2742
101 1910
83 1290
70 918
56 587
47 414
38 361
17.8 (min.) 79
Table 7.3.1: ISVPL-to-output examples
* 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
for details.) Note that the maximum ISVPL setting
of 153 V is greater than the 150 V maximum peak
voltage available from the example PLM 10000Q.
Other models may differ. This is to accommodate
the small degree of production spread of maximum
output voltage that exists between PLMs. By
allowing a maximum ISVPL setting fractionally higher
than the maximum safe output voltage under any
condition ensures that severe clipping will never be
encountered.
PLM Series Operation Manual 19
4 8 16
2926 1463 732
2813 1406 703
1830 915 458
1275 638 319
861 431 215
613 306 153
392 196 98
276 138 69
181 90 45
40 20 10