Circuit Description; G Board; Operation During Power-On Sequence; Circuit Operation - Sony BVM-L230 Service Manual

2-1. G Board

The power block of this unit is a multi-output power board
that consists of a power-factor improvement regulator, two
types of insulating converters, a DC-DC converter having
three circuits on the secondary winding, and two series
regulators.
. Power-factor improvement regulator for conforming to
power harmonic regulations
. SUB5V regulator for supplying power to a control unit
(BKM-16R)
. Main regulator for supplying required power to each
board in a main unit
. DC-DC converter for supplying a 5V_COR voltage to
the B board in a main unit
. DC-DC converter for supplying a 5V_VIDEO voltage to
the B board in a main unit
. DC-DC converter for supplying a 5V_OP voltage to the
B board in a main unit
. Series regulator for analog circuit on the B board in a
main unit (+A5 V)
. Series regulator for analog circuit on the B board in a
main unit (_5 V)
. LCD unit (T-CON board) driving output

2-1-1. Operation during Power-on Sequence

When power is supplied from an AC input connector
(CN6001) and AC-SW is set to ON, a direct current (DC)
voltage is produced using a rectifier diode (D6000) and
smoothing capacitor and an operating voltage is applied to
a SUB5V regulator (IC6300).
In other words, a SUB5V regulator unconditionally
operates when the power is turned on. A main regulator
and power-factor improvement regulator (PFC circuit)
automatically begins to operate when this SUB5V
regulator operates.
Each power circuit on the secondary winding begins to
operate about 0.5 seconds after a main regulator operates.
BVM-L230
Section 2

Circuit Description

2-1-2. Circuit Operation

1. SUB5V regulator
SUB5V power mainly consists of PWM switching circuit
IC6300 (power IC), PH6300 (isolator), T6300 (SUB5V
transformer), and a rectifier circuit on the secondary
winding of T6300. IC6300 incorporates a PWM controller
and protection circuit.
A voltage is supplied to the Vcc pin through the internal
resistor of IC6300 when an operating voltage is applied to
the ST pin of IC6300 through T6300.
When the voltage rises to the operating start voltage of IC,
the switching operation of internal FET starts and a
SUB5V voltage is produced from the secondary winding
of T6300. The component compared with the reference
voltage of IC6301 is produced as a feedback voltage using
PH6300. As a result, stable operation is continued.
Simultaneously, a VCC voltage (of about 16 V) is
generated on the tertiary winding of T6300 and supplied as
the operating power of each IC on the primary winding.
2. Power-factor improvement regulator
The power-factor improvement circuit system of this
power supply employs a current critical-type boost chopper
system. Therefore, output voltage Vpfc already becomes
higher than the peak value of an input supply voltage.
Output voltage Vpfc of this unit is set to about 390 V.
A power-factor improvement circuit consists of IC6502
(power-factor improvement IC), L6002 (PFC transformer),
C6006 (smoothing capacitor), D6506 (boost diode), Q6500
(FET), and an input/output voltage detector and its related
parts.
For basic operation, when Vcc power is supplied to
IC6502 through PH6400 and Q6400 after SUB5V power
operates, Q6500 is turned on and a current flows through
the primary winding of L6502 and Q6500. This current
increases due to the inclination of Vin (rms)/L. L in this
case is an inductance value on the primary winding of
L6502. This FET current is monitored using source
current detection resistors (R6530 and R6532). Q6500 is
turned off when the FET current reaches the setting value
prescribed using a multiplier in IC6502. At that time, a
current that decrease due to the inclination of (Vpfc-Vin
(rms)/L flows through D6506. Q6500 is turned on when
the current becomes zero. This operation realizes a current
critical operation.
2-1