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3-3. Horizontal output circuit (Diode Modulation)
1) Summary
The horizontal deflection output circuit provides Diode
Modulator funciotn which is for E-W Correction.
2) Circuit Diagram
Cy
Di
-Iy
Q2
Cy1
Di1
-Im
3-4. Vertical output circuit
1) LA7838(IC301) Block Diagram
Vert.
Trig
input
FBT(1st)
Iy
Ly
Cs
Vs
Lm
Im
Q1
Vm
Cm
Ramp
generator
Vert.
One
shot
control
Multi
S/W
1
2
3
4
3) Description
The modulation of the horizontal deflection current at a
vertical rate is accomplished in the following manner. During
the first part of the scanning period, diodes Di1 and Di are
functioning as energy recovery diodes for the energy stored
in both the balance coil Lm and the horizontal yoke. in this
mode, the cathodes of both diodes are clamped to ground.
During the second part of the scanning period with the Q2
+
B
on, these diodes are once again connected to ground. As a
result, the scanning voltages for the balance coil and the
yoke are equal to the voltages accross capacitors Cm and
Cs respectively. The total voltage accross both of these
capacitors is kept constant byt since the voltage accross
Cm is modulated by the voltage at Q1's emitter, it follows
that the voltage across Cs is modulated in the opposite
phase. The deflection current is modulated as a result since
it is a function of scan voltage. During flyback the energy in
SPCC
the yoke and the balance coil is stored in CY and CY1. since
the total inductance (Lyoke + Lm) is constant and Lyoke ×
CY is equal to Lm × CY1 (due to equal resonance
frequencies), the flyback or retrace time is independent of
the modulation. Also, with the main B
constant, the total flyback voltage at the collector of the Q2
will also remain constant and thus avoid modulating the high
voltage.
Vert.
Drive
size
Pump up
Vcc
5
6
7
8
- 30 -
Thermal Protection
Vert.
Drive
9
10
11
12
+
volt supply remaining
13
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