Advertisement
. :or Circuit
-·~
+e>--~
loo)
=
Ll01
LOT
PA Board
CN904
CN2
II
HV RTN
II
4
ABL I
D902
TP502
ABL2
'
tN902
FBTIHI
FBTCtl
tN904
9
HY PROT
tN90J
R53t
I
H STAT
· J
TO t BOARD
2
G2 OUT
tN905
Df"X
DFX
DFY
Df"Y
tN906
HEAlERl-1
J
TO t BOARD
HEATERl+I
FOCUS
PACK
• High Voltage Current Protector, ABL Circuit
+B
CONTRAST
BK Board
PC
TO CRT
) TO t BOARD
3-25
IC501
9 ORV
PWM CONTROL
ON/OFF
8
D513
3-6. Power Supply Circuit Descriptions
(G Board, GA Board, GB Board, and
GC Board)
1. RCC Switching Regulator (IC4 and T5)
The blocking oscillator is composed of IC4 and T5 (SRT).
Immediately after the Main Power switch at the rear is turned
on, first the regulator starts up because IC4 operates and
generates the 5V voltage for DIGITAL, +12V voltage, and -
12V voltage at the secondary side of T5. At the same time, the
18V voltage (For PFC CTRL IC) and 15V voltage (For half bridge
switching regulator) are generated at the primary side
of
T5.
2. PFC Switiching Regulator
The power factor improvement circuit is composed of I Cl, Q5,
DIO, T3, C28 of the G board, the GC board, and related parts.
The power factor improvement circuit (referred to as PFC
hereafter) of this power supply adopts the boost PWM control
method. As it basically operates as the boost switching regulator
in continuous current operation, the output voltage Vpfc is
always higher than the peak value of the input power supply
voltage. As the input voltage is a sine wave, in ·addition to
voltage control, it controls current in proportion to the input
voltage.
IC! not only keeps the Vpfc voltage constant but also PWM-
controls Q5 so that the current flowing to T3, that is the main
power ·supply current is similar to the input voltage waveform.
As a result, the power factor is improved because the input
current and input voltage waveforms are similar.
The GC board is composed of ICl, Ql, and the output voltage
detection resistor. It creates a control signal which varies Vpfc
in proportion to the input power supply voltage, and supplies
them to ICl. This reduces the loss of QS and T3.
3. PFC OVP Circuit
The comparator of IC2 (1/2) is an OVP circuit for protection
when the Vprc rises abnormally in the malfunction of the
feedback system of the PFC CTRL.
Normally, the output of this comparator is "LOW". It becomes
"HIGH" when OVP operates. Consequently, Pin@) of ICl
(ENABLE pin) becomes "LOW" via the latch of Q3 and Q4 to
stop the PFC switching. At the same time, D21 (red LED) is lit
to inform of the error.
4. Half Bridge Switching Regulator
(06, 07,_T4, GA Board IC101, IC102)
The voltage obtained by dividing the PFC output voltage by two
at C29 and C30 is used as the power supply of T5. The +B
feedback voltage from IClOl of the G Board is given to IC102 ·
of the GA board which is passed through isolator PCI. The
PWM pulse generated at IC102 of the GA board is passed
through the DRIVER IC (IClOl) to switch between Q6 and Q7
alternately. As the result, +6V, -6V, +15V, -15V, and +B
voltages
are
generated at the secondary side of T4.
5. Power Supply Control
In the standby state, only the RCC switching regulator and PFC
switching regulator operate. In this state, when the POWER ON
signalfrom the sub CPU (IC7001) of the E board becomes
"LOW", Q104 goes OFF, the LED inside the isolator PC2 lights
up, and the photo-resistor turns ON. As Ql2 is ON the rush
current protection resistor R2 is short-circuited by RY2, Pin®
of PC2 becomes "LOW", QlOl of the GA board goes OFF,
IClOl oscillates, and H.B operates.
6. PFC Failure Detection Circuit
The circuit which monitors if the PFC circuit is operating
normally is composed of IC106, Dl 13, DI 14, and other circuit
parts.
The pulse generated at the secondary side of T3 (PFCT) is
rectified by Dl 13 and Dl 14, input to the(±) terminal of the
comparator (IC106 (2/2)), and compared with.the reference
voltage. When PFC is not operating, the comparator output
(PFC FAILURE) becomes "LOW" because the comparator(±)
terminal voltage cannot reach the reference voltage. Normally,
D 112 (green LED) is operated to indicate that operations are
carried out normally.
3-26
7.
OVP (Over voltage protection), OCP (Over
current protection) Circuits (GB)
• OVP (Over voltage protection) circuit
The voltage of each power supply line is compared with the
reference voltage by the comparator of the GB board to detect
over voltage.
The output of each comparator is normally "LOW" and
becomes "HIGH" when errors occur.
• OCP (Over current protection) circuit
Over current is detected by supplying the voltage generated
when the current detectio~ resistor is inserted in each power
supply line and current is passed through this resistor to the
comparator of the GB board.
The output of each comparator is normally "LOW" and
becomes "HIGH" when errors occur.
8. SHUT DOWN Circuit
(0301 to 0312 of GB Board)
When the PFC FAILURE signal becomes "LOW" or when the
OVP or OCP signal works so that the SHUT DOWN signal
becomes HIGH, Q!05 of the G board turns ON and the
operations of the half bridge switching regulator stop.
In
this
circuit, the OVP and OCP signals are latched and input to the
encoder.
9. Encoder (GB Board)
A total of 11 signals (5 OVP signals, 5 OCP signals, and one
PFC FAILURE signal)
are
encoded into-4-bit signals, to inform
the sub CPU (IC902) of the E board of errors.
10. CRT Protector
If
the horizontal/vertical deflection circuits stop due to some
reason, the E PROT signal from the E board becomes "HIGH".
As a result, Q103 of the G board turns ON and the operations of
the half bridge switching regulator stop.
Advertisement
