1-2. H V Voltage Circuit
H V generator circuit (Fig 1-2-l)
H V generator circuit is composed on
Q515,
C530,
C531,
and FBT T503.
This circuit generates the
flyback
pulse. This pulse level is
450-55OVp-p.
This
flyback
pulse is boosted up to the high voltage (24 KV) by FBT.
The High voltage is supplied to the anode of CRT from FBT.
H V drive circuit (Fig l-2-2)
This circuit generates the drive pulse for FET
Q515
in H V generator circuit.
The input of
IC501
(pin
0)
is supplied a trigger pulse from T502 of H deflection circuit.
IC501
outputs the drive pulse of FET
Q515,
and Toff (See Fig l-2-3) of
IC501
output pulse is decided
10µS
by
R530
and C528.
The output pulse of
IC501
is supplied through emitter follower Q553, AC coupling capacitor C529 and buffer amp of
Q513,
and
Q514
to FET
Q515.
H V generator or DC/DC converter circuit (Fig 1-2-l)
This
DC/DC
converter circuit is composed of a step down chopper, FET drive and control circuit.
This chopper circuit is composed of L507, D518 and C539.
This circuit supplies
DC
voltage of 35-l 20V to FBT for H V regulation.
The relationship between output DC voltage of chopper circuit and horizontal frequency is shown in Fig l-2-6
The FET drive circuit is composed of the buffer circuit of
Q520,
0521,
R571 and level shift circuit of
R544,
C537,
R545,
R582,
D517,ZD507.
The DC level of the output pulse from the control circuit (pin
0
of
IC5A4)
is shifted and is supplied to FET
Q517
by
this circuit. (See Fig l-2-4)
This control voltage is a negative feedback circuit and supplies PWM (Pulse Width Modulation) pulse through FET
drive circuit to FET Q517.
High voltage output is divided by resistors of
R549,
R5E2,
R5E3,
and 450M ohm resistor in FBT.
This divided voltage is supplied to the buffer amp and to the error amp.
The output voltage of the error amp is supplied to PWM circuit of
IC5A4
and
IC5A4
supplies PWM pulse through
FET drive circuit to FET Q517.
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