Logic And Drivers; Oscillator - Toshiba TP43H60 Service Training

Logic and Drivers

As shown in Figure 6, the logic block controls the
MOSFETs' switching frequency. The outputs of
the logic block feed two drivers that are powered
by the start block. After the start-up voltage is
applied to pin 8, the start block supplies a drive
Vcc (DRI Vcc) of approximately 8V to pin 9.
Delaying the driver supplies at start-up prevents
damaging the MOSFETs. The 8V on pin 9 pow-
ers driver B internally. To power driver A, resistor
R862 and diode D862 add the voltage from pin 9
to the voltage on pin 15. D875, C863, D873 and
C873 are voltage regulators and filters for these
supplies.
D873
C873
R862
DRI Vcc
8 9
Vcc
Start
A
B
Figure 6
Logic Circuit
D862
D875
VB
C863
15
Q801
V
IN
1
B+
130V
Out
14
To
T862
COM.
12

Oscillator

Refer to Figure 7. Q801's internal Oscillator de-
velops the power supply's switching frequency by
generating a ramp waveform internally. During
normal operation, both MOSFETs are OFF for a
short time when they are alternately switching. This
OFF time is called dead time and determined by
the value of resistor R867 on the dead time (DT)
terminal pin 7.
Q801
R867
Q801's Internal Oscillator
8
OSC
7 DT
Figure 7