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DEFLECTION PROCESSOR FOR MULTISYNC MONITORS S1D2511B01
33
with C
OSC
: capacitor connected on pin 22
f: synchronisation frequency.
Vertical Moire
By using the vertical moire, VPOS can be modulated from to frame. This function is intended to cancel the fringes
which appear when line to line interval is very close to the CRT vertical pitch. The amplitude pf the modulation is
controlled by register VMOIRE on sub-off via the control bit D7.
DC/DC CONVERTER PART
This unit controls the switch-mode DC/DC con-verter. It converts a DC constant voltage into the B+ voltage
(roughly proportional to the horizontal frequency)necessary for the horizontal scanning. This DC/DC converter can
be configured either in step-up or step-down mode. In both cases it oper-ates very similarly to the well known
UC3842.
Step-up Mode
Operating Description
- The powerMOSisswitched-onduringthe flyback (at the beginning of the positive slope of the horizontal focus
sawtooth).
- The power MOS is switched-off when its current reachesa predeterminedvalue. Forthispurpose, a sense resistor
is inserted in its source. The voltage on this resistor is sent to Pin16 (I
SENSE
).
- The feedback(coming either from the EHV or from the flyback) is divided to a voltage close to 4.8V and com-
pared pared to the internal 4.8V reference(I
VREF
). The difference is amplified by an error amplifier, the output of
which controls the power MOS switch-off current.
Main Features
- Switching synchronized on the horizontal fre-quency,
- B+ voltage always higher than the DC source, - Current limited on a pulse-by-pulse basis.
Step-down Mode
In step-down mode, the Isense information is not used any more and therefore not sent to the Pin16. This mode is
selected by connecting this Pin16 to a DC voltage higher than 6V (for example V
REF-V
).
Operating Description
- The powerMOSis switched-onas for thestep-up mode.
- The feedbackto the error amplifier is done as for the step-up mode.
- The power MOS is switched-off when the HFOCUSCAP voltage get higher than the error amplifier output voltage
Main Features
- Switching synchronized on the horizontal fre-quency,
- B+ voltage always lower than the DC source,
- No current limitation.