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3. DIODE MODULATOR CIRCUIT
Fig. 12-4 shows a basic circuit of the diode modulator used
in the N5SS.
A key point in the N5SS chassis shown in Fig. 12-4 is to
develop a negative pulse at point B.
In this circuit, a current loop of the resonant circuit for
flyback period is shown by an arrow, and the energy stored
in LDY is transferred to resonant capacitors Cr, Crm in
passing through Cr, Crm, Cs when the scanning completes.
As a result, a positive, horizontal pulse as shown in Fig. 12-
5 (a) will appear at Cr, and the current flows into Crm with
the direction as shown. Then a pulse as shown in Fig. 12-5 (b)
develops at the point B.
On the other hand, since constant amplitude pulses across Cr,
as shown in Fig. 12-5, are applied to the primary winding, the
A
DD
Cr
H
OUT
DM
FBT
L
DY
V
Cs Vs
Lm
B
Q460 Vm
Crm
Csm
Fig. 12-4
high voltage of FBT also develops a constant voltage.
When the negative pulse developed at the point B is integrated
with Lm and Csm, its average value appears at Csm as a
negative voltage.
By modulating this voltage to have the parabolic curve with
Q460, a waveform of Vm is obtained as shown in Fig. 12-6.
As a result, the voltage Vs which is the sum of the power
supply voltage VB and the Vm is applied across the S-curve
capacitor Cs. The Vs becomes as a power source for the
deflection yoke, and the waveform modulated in the parabolic
form, as shown in Fig. 12-2 (b), is applied to the horizontal
deflection yoke and corrects the left-right pin-cushion
distortion.
B
88
a) Waveform at point A
b) Waveform at point B
Fig. 12-5
V
B
VS
0
Vm
Fig. 12-6
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