Iris - Sony DSC-S75 Training Manual

Iris

Iris
Operation Operation
LENS ASSY.
IRIS
M
MOTOR
IRIS POSITION
SENSOR
H
LASER UNIT
IR LED's
The iris motor operates as a servo motor and is controlled by the light level falling on the CCD imager.
The iris opening is adjusted by a two terminal servo motor that is controlled by EVR IC207 and the iris drive ICs.
The iris is spring-loaded, which keeps it at minimum open when no control voltage is applied to the servo motor.
•
The control voltage for the iris servo is provided by EVR IC207 and is determined by the average video level
from the video amplifier (not shown).
•
The average video level is compared to a reference level. Video levels higher or lower than the reference will
change the IRIS CTRL drive voltage output from EVR IC207.
•
An average video level below reference increases the IRIS CTRL voltage from the EVR IC and increases
the iris opening.
•
An average video above reference level decreases the IRIS CTRL voltage from the EVR IC and reduces
the iris opening.
Hall Circuit
The mechanical iris position is sensed by a hall effect device that provides iris position feedback via amplifier
IC205 (4/4) to IC501.
Feedback from the hall amp is also applied to the iris drive circuit in the form of negative feedback. This slows
down the iris response and prevents iris over compensation when it is changing size. Without feedback, the
picture brightness levels will oscillate between too light a picture and too dark a picture whenever the iris makes
FR-181 BD.
CN203
12
CAM P 5V
13
17
HALL (-)
BIAS (+)
16
HALL (+)
15
BIAS (-)
14
LD OUT
IC253 LASER
5
GENERATOR
3
PD OUT
CAM
1
P 5V
2
FIGURE 14-2 - F707 LENS ASSY. B
IRIS CONTROL
IC204, IC205,
Q202 IRIS
DRIVE
IC205
HALL
BIAS
-
+
IC205, Q207
GAIN
HALL
CONTROL
GAIN
LEVEL
IC252
Q258
COMP
Q257
LED DRIVE
30
14. DSC-F707 Lens Assembly
HALL
OFFSET
IC207
IC205 EVR
A/D
CONV.
HALL AMP
LD
-
+
FB
IC501
PD
MC CAM
SH
DSP
IR LED ON
15DSC02 1500 10/10/02