ConMed sabre 180, Service Manual

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maximum. The power delivered to the output at
mains voltage zero-crossing is nearly zero. Mains
frequency ripple on RFSUP is controlled strictly
by C2, as in a conventional mains frequency sup-
ply. Capacitor C1 serves to absorb the 100 KHz
peak energy, while C3 serves to minimize the
magnitude of the 100 KHz current drawn direct-
ly from A6T1.
The PFCEN input on U1-11 is used to enable
the switching regulator. It is biased ON via
R12,13 and pulled low to the OFF state by the
microcontroller via A3U22-14. The microcon-
troller enables PFCEN only during activation.
The switcher may be shut down for troubleshoot-
ing by shorting PFCEN at TP14 to ground at
TP13. C21 controls the "slow start" timing to
cause RFSUP to rise with slight overshoot when
PFCEN is enabled. R14 and C19 serve to set the
operating frequency to about 100 KHz. R25,29
and C29,30 set the overall PFC loop gain and
compensation. The PKL input on pin 2Y hard-
limits the switching current to prevent damage to
Q1. VREF on pin 9 is an internal stable reference
source of +7.5Vdc used to set the DC output
voltage on RFSUP.