Date: 10/02/98 R762720
R-G-B Driver
R762720
18
amplitude of 12V. This pulse is added to the
IBCL
lines as these lines are not carrying
any valid information during this time. The
ABL
pulse is here ac coupled to the lines
through C19, C20 and C21.
As the ABL trigger pulse is generated on the
UN SYNC+ VERT DEFL
board and
superposed on the
V BL
(has an amplitude from 17V - 34V), the
V BL
is dropped by
20V with Z3 and Q3 will conduct during this
V BL
pulse time.
The differentiator C18/R70 drives Q4 into conduction for 20µS and via R73/C19, C20,
C21 they are AC coupled into the IBCL lines.
Brightness / Black Level.
Introduction.
The brightness control is about identical to the contrast. The general brightness is
combined with the individual
BLACK_LEVEL_*
and the resulting
OUTPUT_DC_*
volt-
age is an offset of the reference black level of +2V.
At 50% brightness setting, the black level of the output signal of the
RGB DRIVE
board
must be clamped at +2V. This condition is translated into a 2V output for the
potentiometers
VO1, VO2, VO3
of IC1
and
IC2. Only then, there is no current flow in
R7, R8, R9, R10, R11 and R12. The +2V
OUTPUT_DC
is now the same as the refer-
ence voltage of the inverters/sommators (=comparators) IC205, IC305, IC405.
Circuit Implementation.
As
VRN0
= +3V and
VRP0
= +1V the brightness voltage at
VO0
of IC1 changes from
+3V (min. brightness) to +1V(max. brightness). This brightness voltage is applied again
to the
VRP1,2,3
of three potentiometers in IC1. The other end
VRN1,2,3
of these
potentiometers is the reference voltage
+2V.
These three potentiometers in IC1 obtain the same settings of the gain controls in IC3.
If now the brightness voltage is +2V (50%) the outputs
VO1,2,3
of IC1 are ALWAYS at
+2V, irrelevant the gain setting.
Any change of the brightness and gain settings change the output voltage(s). With
above
gain scaled brightness voltages
the black level is tracked with the gain
adjustment in order not to deteriorate the colour temperature with contrast.
We can however add to these gain scaled brightness voltages an extra offset via R10,
R11, R12 to adjust the low lights.
Technical description
Summary of Contents for GRAPHICS 1209S
Page 4: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC SAFETY NOTICE...
Page 9: ...BARCO PROJECTION SYSTEMS GRAPHICS 1209S 90 00972 230V AC 90 00977 120V AC GENERAL INFORMATION...
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