Crown XLS1000 - Page 35

kHz, one quarter the amplifier switching frequency. The synchronization is necessary to
prevent beat tones from forming in the amplifier output stage.
A 192 kHz balanced square wave signal is generated on the APM and is routed to the
main board via J700B pins #24 & #25. Q909 resets the timing cap (C944) on the +5V
control IC (U905) when the “CLKP192K” signal rises, forcing the control IC to operate
at this frequency. Optocoupler (U906) transfers the clock signal from the secondary
ground referenced side to the primary AC line referenced side. Transistor Q910 turns on
when the Optocoupler output voltage rises, when this happens C947 is charged as the
emitter voltage drops. This forces U902, the main supply control IC to follow
synchronization signal.
Fan Driver Circuit
A variable speed 12V fan is controlled by the uP via the fan driver circuit. The fan driver
uses a simple NPN (Q907) pass transistor and a feedback control loop (U904) to regulate
the voltage applied to the fan to four times the “FAN” drive voltage. The feedback
control loop is purposely slow responding so that it does not react to the impulsive motor
currents drawn by the brushless DC fan motor. This isolates –LV supply from these
noise currents, yet precisely regulates the fan to desired voltage.
BOM: 141581-5_A XLS1500/120V MAIN PWA
REF.
DES.
CPN
DESCRIPTION
MAP
LOC.
C1 135505-1 CAP, 0.1UF 25V 10% X7R 0603 C 2
C2 135505-1 CAP, 0.1UF 25V 10% X7R 0603 C 2
C3 139719-1 CAP, 1.0UF 25V X7R 10% 0805 C 1
C4 139719-1 CAP, 1.0UF 25V X7R 10% 0805 C 1
C5 135505-1 CAP, 0.1UF 25V 10% X7R 0603 K 1
C7 139719-1 CAP, 1.0UF 25V X7R 10% 0805 C 2
C8 139719-1 CAP, 1.0UF 25V X7R 10% 0805 C 2
C10 OPEN C 5
C11 139719-1 CAP, 1.0UF 25V X7R 10% 0805 B 2
C12 135505-1 CAP, 0.1UF 25V 10% X7R 0603 G 4
C13 135505-1 CAP, 0.1UF 25V 10% X7R 0603 C 2
C14 103429-474K8 CAP, 470NF 250V 10% X7R 1812 I 3
C15 C 4477-3 470 UF 35V VERT I 3
C16 A11427-104K2 .1UF 50V CHIP CAP 10% 0805 X7R E 2
C17 135505-1 CAP, 0.1UF 25V 10% X7R 0603 C 2
C18 135505-1 CAP, 0.1UF 25V 10% X7R 0603 E 2
C19 139947-1 CAP, 10UF 10V 10% X5R 1206 C 1
C20 135505-1 CAP, 0.1UF 25V 10% X7R 0603 C 1
C21 139947-1 CAP, 10UF 10V 10% X5R 1206 C 1
C22 135505-1 CAP, 0.1UF 25V 10% X7R 0603 C 2
C98 135505-1 CAP, 0.1UF 25V 10% X7R 0603 B 2
C100 135505-1 CAP, 0.1UF 25V 10% X7R 0603 B 5
C101 135505-1 CAP, 0.1UF 25V 10% X7R 0603 B 5