Toshiba TW40F80 manual Diode Modulator Circuit

2. DIODE MODULATOR CIRCUIT

In N5SS, the distortion correction is carried out by the ditigal convergence circuit. So the component of the diode modu- lator circuit is the same as that of conventional television, because it is used only for the horizontal oscillation adjust- ment.

Fig. 10-2 shows a basic circuit of the diode modulator used in the N5SS.

A key point in the modulation circuit shown in Fig. 10-2 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. 10-3 a) will appear at Cr, and the current flows into Crm with the direction as shown. Then a pulse as shown in Fig. 10-3 b) develops at the point B .

On the other hand, since constant amplitude pulses across Cr, as shown in Fig. 10-3, are applied to the primary wind- ing, the high voltage of FBT also develops a constant volt- age.

A

			FBT
	LDY
DD	Cr
H
OUT	Cs	Vs	VB
	B Lm
DM			Q460 Vm
	Crm		Csm

Fig. 10-2

When the negative pulse developed at the point B is inte- grated with Lm and Csm, its average value appears at Csm as a negative voltage.

By modulating this voltage with Q460, a waveform of Vm is obtained as shown in Fig. 10-3 b). 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 be- comes as a power source for the deflection yoke as shown in Fig. 10-4, is applied to the horizontal deflection yoke.

0

a) Waveform at point A

0

b) Waveform at point B

Fig. 10-3

VB

VS

0

Fig. 10-4

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