Toshiba TW40F80 manual Output stage power supply voltage

(4)To decrease the collector loss of Q3, the power supply voltage is decreased during scanning period as shown in Fig. 8-7, and VCE1 decreases and the collector loss of Q3 also decreases.

Q3 Collector loss decreases by amount of this area

Power supply

for flyback period (Vp)

Power supply

for scanning period (Vcc)

Scanning period

Flyback period

Fig. 8-7 Output stage power supply voltage

(5)In this way, the circuit which switches power supply circuit during scanning period and flyback period is called a pump-up circuit. The purpose of the pump-up circuit is to return the deflection yoke current rapidly for a short period (within the flyback period) by ap- plying a high voltage for the flyback period. The basic operation is shown in Fig. 8-8.

(6)Since pin 7 of a transistor switch inside Q301 is con- nected to the ground for the scanning period, the power supply (pin 3) of the output stage shows a voltage of (VCC – VF), and C308 is charged up to a voltage of (VCC – VF – VR) for this period.

(7)First half of flyback period

Current flows into L462 + L465 + L464 ® D1 ® C308

®D308 ® VCC (+35V) ® GND ® R305 ® C306

®L462 + L463 + L464 in this order, and the voltage across these is:

VP = VCC + VF + (VCC – VF – VR) + VF about 63V is applied to pin 3. In this case, D301 is cut off.

(8)Last half of flyback period

Current flows into VCC ® switch ® D309 ® C308 ® Q301 (pin 3) ® Q3 ® L462 + L463 + L464 ® C306 ® R305 in this order, and a voltage of

VP = VCC – VCE (sat) – VF + (VCC – VF – VR) – VCE (sat), about 56V is applied to pin 3.

(9)In this way, a power supply voltage of about 35V is applied to the output stage for the scanning period and about 63V for flyback period.

D301	C308
	D308
Q301
6	3
	D309	R308
	Switch
Q3	7
D1
	L462+L463+L464
	2	+
Q4
		C306
		R305

D301	C308
	D308
Q301
6	3
	D309	R308
	Switch	VR
Q3	7
D1		First half
	L462+L463+L464
	2	+
Q4
		C306
		R305

Last half

(a) Scanning period (b) Flyback period

Fig. 8-8

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