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1.4
High voltage block
The high voltage circuit is composed of the high-voltage regulator IC701, MOS-FET Q701
flyback transformer (FBT) T701, operation amplifier IC702 and their peripheral circuits.
1.4.1
High voltage control circuit
The IC701 is an IC for high voltage control, with the block diagram given in Fig.13. The OFF trigger PWM
control system is adopted to carry out high voltage control. The built-in VCO circuit gets synchronized
when the horizontal synchronous signal (hereafter SYNC signal) is input from Pin 3 of IC701 (horizontal
synchronous input terminal). Thus, the MOS-FET Q701 is controlled to turn OFF with the timing of the
SYNC signal changing over to HI, and is called OFF trigger system.
Further, the DC voltage, output after the feedback signal (IC701 Pin 11) from FBT T701 is compared with the
high-voltage set voltage (IC701 Pin 12) from IC101 in the internal error amplifier, is compared with the saw-
tooth-waveform of VCO to control the pulse output DUTY so as to keep the high voltage constant (PWM control).
The timing chart for OFF trigger PWM control system is given in Fig.14. Set the high voltage by selecting
[HVADJ] in OSD and manipu/- button (Standard value: 27.0kV).
1.4.2
Protective function circuit
(1) Start and stop of high-voltage regulator IC701
The IC701 starts operation when Vcc voltage (power voltage applied to Pin 2 and Pin 10) attains the
level of 8.4 Vtyp, and the operation stops when the Vcc voltage is less than 7.4 Vtyp.
(2) IC701 overcurrent protection (OCP) function
It detects the peak value of the drain current in MOS-FET Q701 per pulse and stops DRIVE when the
voltage in Pin 6 of IC701 detecting the end-to-end voltage of the source resistors (R706 and R707),
exceeds 1.0 Vtyp until the next SYNC signal is input.
(3) IC701 overload protection (OLP) function
This function brings the system to the latch stop when OCP gets continuously activated due to
continuous overload.
It forms time constant using C716. With OCP activated and C716 charged and the voltage in Pin 8 of
IC701 exceeding 2.5 Vtyp, IC701 gets set to Latch mode, bringing the control operation to stop. This
status does not get released (reset) until the Vcc voltage (power voltage applied to Pin 2 and Pin 10)
in IC701 is less than 7.4 Vtyp.
(4) Over-voltage protection function for anode voltage (X-ray protector)
A voltage proportional to the high voltage is generated in Pin 6 of T701 due to the winding ratio
between secondary and tertiary winding inside FBT T701. This voltage is then rectified by D707 and
C708 and is further divided by R708 and R709 before being input in Pin 17 of microcomputer IC101
for comparison with the X-Pro set value. In case the voltage exceeds the set value, the output in Pin
33 of microcomputer IC101 gets fixed to LOW (P-OFF mode). With the mode set to P-OFF, the
application of voltage Vcc to IC701 stops, causing the IC701 operation to stop. The status continues
until the power SW is turned OFF. The overvoltage protection function is set to operate when the
high voltage level reaches 30kV (with the beam current is approx. 1mA).
(5) Overcurrent protection function for beam current (beam protector)
The beam current is supplied from +12V power source through R722. Since the end-to-end voltage of
R722 varies according to the beam current, the voltage drop due to R722 becomes large if the beam
current increases. The voltage in Pin 9 of FBT T701 (the voltage obtained by subtracting the voltage
drop due to beam current from the +12V power voltage) undergoes resistance division by R723 and
R724, and is then input into Pin 6 of operation amplifier IC702 for comparison with Pin 5 of IC702
(reference voltage). The voltage is then output (Pin 7 of IC702) and is input into Pin 16 of microcom-
puter IC101. The voltage in Pin 7 of IC702 (output terminal) is output linearly due to the fluctuation in
beam current. However, if the terminal voltage in Pin 16 of IC101 exceeds Beam-Pro setting value (ABL
data +70 : Max. 254), the output of Pin 33 of IC101 gets fixed to LOW (P-OFF mode). With the mode
set to P-OFF, the application of Vcc voltage to IC701 stops, causing the IC701 operation to stop. This
status continues until the power switch is turned OFF. The overcurrent protection function is set to
operate when the beam current reaches the level of approximately 1300
µ
A.
Summary of Contents for MultiSync FP1355 FP1355 FP1355
Page 23: ...1 17 Q502 Q502 Damper diode Current waveform fh 106k ...
Page 25: ...1 19 Q502 Q502 Damper diode Current waveform Q502 Ic Q502 Vce ...
Page 58: ...1 52 Figure 25 IC211 MC13289ASP block diagram ...
Page 63: ...1 57 Figure 30 IC212 XC3824P2 block diagram ...
Page 65: ...1 59 1 11 Wave form of main circuit voltage ...
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Page 120: ...MultiSync FP1355 User s Manual ...
Page 144: ... VSP C0464 REVISE 2 ...
Page 166: ...Fig 2 BEZEL LOGO VSP C0464 COLOR OF LETTERING Kingfisher Blue 6704 11 5 24 5 66 ...
Page 169: ...VSP C0464 Fig 5 1 PRINTING SPECIFICATION OF CARTON BOX North America ...
Page 170: ...VSP C0464 Fig 5 2 PRINTING SPECIFICATION OF CARTON BOX Europe ...
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