10
QSC Audio Products LLC
Application Engineering Team
Because the current needs of the device are compressed into a very narrow conduction angle, the peak values of the
current can be excessively high. High current peaks cause two types of problem in the AC system itself: power loss (I
2
× R) in the wiring, which becomes heat in the wires, outlets, etc.; and distortion because of nonlinear voltage drop (I ×
R), which squashes the tips of the voltage waveform. The high harmonic content of the current peaks sometimes causes
noise radiation issues.
Concern about the pervasive effects of nonlinear power supplies has even led governmental and international agencies to
establish limits and standards on power factor in electronic products, especially those that draw large amounts of current.
The narrow conduction
time in the rectifiers
of a non-PFC power
supply, above, results
in sharp current peaks,
below.
Power factor correction
An advantage of switch-mode power supply technology used in the PLD4.3 and PLD4.5 amplifiers is that we design
power factor correction into them; the current flows throughout the whole voltage waveform and not only at the peaks.
Conventional, non-switch-mode power supplies cannot do this in a practical way.
Power factor correction, as employed in the power supply of these two models, makes the current waveform more nearly
sinusoidal to closely match the AC voltage and achieve power factor figures of at least 0.9 (and even upwards of 0.95 un-
der heavy duty). This practically eliminates any significant harmonic currents and voltage waveform distortion, and reduces
current peaks as well.
In its class of professional power amplifiers, only the PLD Series from QSC offers power factor correction in any models.
