1-4. Low voltage chopper regulator circuit
The low voltage chopper regulator circuit id PWM controlled and synchronized with the H deflection DC/DC
converter output of the DC/DC converter.
The pulse duty is determined by comparing the saw tooth waveform and the feedback voltage through error amp of
IC5A4 with a comparator of IC5A3. This feedback circuit is automatically controlled and generates constant and
stable output voltage.
If the H OSC operation stops, the output voltage will become low. The output voltage of 6V line is limited by low +B
protector.
This circuit generates 6V power supply from the pulse of T551’s primary winding and 5V power supply from the 6V
power supply by using 3 terminal regulator of lC864. By using the pulse induced in the secondary windings, 12V,
- 1 OV, -5V and horizontal raster centering power supply can be obtained.
As for 12V power supply, it is obtained as below.
After adding the pulse induced between pin
of T551 and the gen 6V, it is rectified by D553 and
C 5 6 1 .
Then the rectified voltage of 13V or a little more voltage is obtained. 12V power supply is obtained from this voltage
by using 12V 4 terminal regulator of lC552.
As for -lOV power supply, it is obtained by rectifying the voltage induced between pin
of T551 by D552 and
C559. As for -5V power supply, it is obtained by using zener diode and as for horizontal raster centering power
supply, it is obtained by rectifying the voltage of pin
and pin
with their middle point (pin
connected to the
+B voltage of horizontal deflection.
The voltage of pin
is rectified by Q513 and C517. The voltage of pin is rectified by D512 and C516.
Q552
T551 L551
+24V
Low +B
0551
IC5A3. R5G7
VR551
+6V ADJ
R5F9
R5GO
SAW TOOTH
1C5A5
H OSC
GENERATOR
+24v
(Fig 1-4-1) BLOCK-DIAGRAM of the Low Voltage Chopper Regulator
47
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