6-7
6-4. C Board Descriptions
1. Screen (G2) voltage regulator
The G2 regulator circuit composed of IC601 (1/2), Q601 and
Q602 is controlled by the G2 control voltage from the BK
board and supplies the G2 voltage which optimizes the CRT
cathode voltage. This board uses a high voltage obtained by
rectifying the drain pulse voltage of Q555 of the E board at
D555 and C558.
2. Blanking Circuit
The blanking signal from the BK board is amplified by IC701,
clamped to –12V by D501, and supplied to G1 of the CRT.
6-5. Power Supply Circuit Descriptions
(G Board)
The power supply of this unit is composed of the following
three switching regulators.
1. Power-factor correction regulator for conforming to the
power supply harmonic regulation
2. LOW-B regulator for supplying the voltage required by
the processing circuits of the signal block and deflec-
tion/high voltage blocks mainly
3. HIGH-B regulator for supplying voltage required by the
output circuits of the deflection/high voltage blocks
1. Power-factor correction block
The power-factor correction circuit (hereafter referred to as
PFC) is composed of T3, IC31, Q31, D36, C43, and related
parts.
The power-factor correction circuit of this power supply
adopts the boost PWM control method. In the basic opera-
tions, the output voltage Vpfc is made higher than the peak
value of the input power supply voltage at all times by the
boost type switching regulator which performs continuous
current operations. Unlike the normal regulator, as the input
voltage is a sine wave, voltage control and current control
proportionate to this are performed. Consequently, IC31
which PWM controls PFC not only makes the Vpfc voltage
constant but also PWM controls Q31 which is the FET for
PFC OUT so that the current flowing to T3 (input power
supply current waveform) becomes the same as the input
power supply voltage waveform.
As the waveforms of the input voltage and current become
similar, the power-factor is improved.
2. LOW-B Regulator
The power supply for LOW-B is mainly composed of IC201,
IC203, PH201, Q205, T201, and T201 secondary rectifica-
tion circuits.
IC201 which is a PWM control IC is added with the control
voltage from IC203 which performs constant voltage con-
trol of the +15V line via the isolater PH201. The Q205 FET
which is the output from the converter is switched by the
pulse PWM controlled by IC201 via the Q203 and Q204
buffers. As a result, at the secondary side of T201, +7V for
the standby +5V and +6V/–6V/+15V/–15V which are re-
quired by each board are generated.
The standby +5V voltage is generated by IC202 which is an
error amplifier and Q207 which is a pass transistor. The power
supply voltage lines supplied to each board are incorporated
with transistor switches to reduce power consumption dur-
ing standby.
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