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(g) Overvoltage protection
If some failure occurs and the 24 IV] line output increases beyond 29 [V], the voltage at the
output is sensed by the Zener Diode ZD658.
This Diode (ZD658) will activate the LED within the photocoupler PC602, turning on the
transistor within it. Once the transistor is on, pin 6 of IC601 will go high, stopping the oscilla-
tion within this IC.
-------~J
K3 +24V
ZD658
PC602
-
IC601
-
' - - - - - + - - - - - u K4 GN D
(Fig. 2-1-7) Overvoltage Protection Circuit
(2-1-2) MAIN DC/DC CONVERTER (d)
This converter's output is the power source for the Flyback Transformer. It is controlled by PWM
method and synchronized by the Horizontal OSC. output.
Output voltage of this converter is varied in respect to Horizontal OSC. frequency so that the
voltage level of the Flyback pulse is constant for any frequency. This Constant Voltage level will
also produce a constant Horizontal Raster size for any frequency. If H.OSC. stops the output of this
converter will become low (in order to protect the CRT beam spot).
The relationship between Output Voltage and H.OSC. frequency is shown in Fig. 2-1-2a.
BLOCK DIAGRAM of this regulator is shown in Fig. 2-1-2b.
150
2
100
LU
1- l'.l
::J
<(
a..
I-
I-
_J
50
:JO
O>
0
15
20
25
30
35
40
fH
(kHz)
(Fig. 2-1-2 a) Relationship between the Output Voltage and the H.OSC. Frequency.
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