Crown k1 Manual Suplementario

K Series Service Manual

Rev A.

Theory  3-3

©1999 Crown International, Inc.

gates. This results in disrupting of the signal path.

The output of U101 is balanced and forms the posi-
tive portion of the output waveform (Vp). The output
of U103 is balanced and forms the negative portion
of the output waveform (Vn). These two balanced sig-
nal lines are routed to the output stage drivers, U02
and U52.

The 250KHz triangle wave has its origins from the
4MHz generator. After entering the divide-by chip (U5),
a 500KHz output signal (pin 9) is routed to U12B. The
output of U12B is a 250KHz square wave.

The 250KHz signal is then sent through U2C. U2C is
a linear IC with R186, R187, C153 and C154 in its
feedback loop. This stage converts the 250KHz
square wave into a triangle wave. From Pin 8 of U2C
and through C152 the 250Kz triangle wave is sent to
U105 which has two functions: gain and high fre-
quency filtering. C150, C151 and R162 serve to filter
the triangle wave signal.

The output of U105 is the 250KHz signal that is routed
to the positive and negative modulators, U101 and
U103.

The Proportional Vcc generator outputs a DC voltage
that varies as the ±Vcc levels vary. This varying DC
voltage influences the 250KHz output level. Because
output signal gain in a PWM amplifier can deviate as
VCC varies a DC voltage proportional to the Vcc sup-
plies is applied to the Triangle generator circuit.

U3C functions as the Proportional Vcc generator.
Through a resistor dropping network (R23/R24) +Vcc
is applied to the non-inverting input. Through another
resistor dropping network (R22/R21) –Vcc is applied
to the inverting input. On the output of U3A is a DC
voltage of 6.2VDC.Through diode D21 and resistor
R20  5.1VDC is applied to U12B.

The modulated 250KHz signal exits the main module
and enters output assembly by means of U02 (Vp)
and U52 (Vn). U02 and U52 are optically coupled
gates giving electrical isolation from main module cir-

cuitry. The output of U02 and U52 are then sent to the
output MOSTFET drivers.

U03A, U03B, U53A and U53B are dual inverting high
speed drivers designed to interface low current digi-
tal circuitry (U02 and U52) with power MOSFETs.
U03A, U03B, U53A and U53B are used to drive the
gates of the output FETs (Q1-Q4, Q51-Q54).

The output stage is divided into two sections, positive
and negative. The signal is then routed to the BCA
filter inductors (Ln and Lp) and the current sense re-
sistors (R13/R14 and R63/R64). The combining point
is then sent to the Output Filter.

With no audio modulation both negative and positive
FET stages conduct. The frequency, phase and am-
plitude of output FET conduction is identical. Since
the FET conduction signals are the same but oppo-
site in polarity complete cancellation takes where the
BCA filter inductors and current sense resistors con-
nect. As the fundamental center frequency (250KHz)
is modulated with audio differences in frequency,
phase and amplitude appear and audio output de-
velops from the BCA filter. This signal is then routed
back to the Output Filters located on the main mod-
ule.

The output filter is made up of three individual filters:
a 250KHz filter (L101/C127), a 500KHz filter (L102/
C131) and a final 250KHz filter. The signal passes
through these three filters to eliminate both any re-
sidual 500KHz and 250KHz signals. The audio signal
is the connected to the output speaker connectors.

Audio output current levels are monitored by the use
of transformer T100. A small primary winding is in
series with the output line and the secondary devel-
ops a voltage related to the output current of the am-
plifier. This output current information is used for two
purposes:

1. Negative feed back.

2. Current feedback information for the Triangle wave
generator.

To prevent excessive output current the K series am-