Overvoltage Protection Circuit And Overcurrent - Sony BVM-L230 Service Manual

2-1-3. Overvoltage Protection Circuit and
Overcurrent Protection Circuit
An overcurrent protection and overvoltage protection
circuit are provided in the PFC voltage line on the primary
winding, and the voltage lines and SUB5V line on the
secondary winding. These circuits protect the power
supply when load is defective. They also protect the power
supply and load when a voltage feedback system is
defective.
The overvoltage protection circuit of a PFC voltage on the
primary winding is detected by comparing the voltage
sensed using a voltage-dividing resistor and the reference
voltage using IC6401. It operates a protection circuit
consisting of Q6454 and Q6455 and stops the operation of
a main regulator. (The setting voltage is approx. 450 V.)
The overvoltage protection circuit on the secondary
winding is detected using a Zener voltage of D6407. It
operates a protection circuit consisting of Q6403 and
Q6404 and stops the operation of a main regulator. (The
setting voltage is approx. 14 V).
The overcurrent of each voltage line is protected using
each current detection circuit. The overcurrent protection
circuit of a PFC circuit is detected by setting the voltage of
a current detection resistor (consisting of R6530 and
R6531) that flows through FET (Q6500). It lowers an
output voltage.
By this operation, a PFC voltage is put into the reduced-
voltage state. A reduced-voltage monitoring circuit
(IC6402) and protection circuit operate, and the POWER-
ON state is canceled to stop the power operation.
The overcurrent protection circuit of a main power circuit
detects the current flowing through a resonance capacitor
(C6112) using R6121 and R6122 and stops the operation
of IC6100.
The overcurrent protection circuit of a SUB5V line detects
the current flowing through FET in IC6300 using R6303
and R6304 and shifts the operation of IC6300 to the
standby mode to lower an output voltage. This state is
restored if load returns to the normal state.
The overcurrent protection of a DC-DC converter in each
line is stopped by the current value set using a function that
is incorporated into each IC.
BVM-L230
The overcurrent setting value of a 5V_CORE line is
approx. 5.3 A.
The overcurrent setting value of a 5V_OP line is approx.
6.5 A.
The overcurrent setting value of a 5V_VIDEO line is
approx. 9.5 A.
The overcurrent protection circuit of a series regulator for
analog circuit power on an option board stops an output
voltage using the protection function (drooping
characteristics) of IC.
2-3