Sony MCC-3000MT Service Manual page 19

2. Operation of 12 VDC output system and protection function
The DC/DC converter function for 12 VDC output consists of a power IC and a peripheral circuit. The 12 V power
output system is divided into the following three channels.
Output system:
• One channel to the KY-687 board
• One channel to the AVP-18 board (Camera A side)
• One channel to the AVP-18 board (Camera B side)
The output protection function works as follows.
• Protection of output overvoltage: When the output power voltage rises to approx. 16 V, the main converter IC
function is disabled and the 12 V output is shut off. At this time, the LED_ALERT signal is output. Automatic
reset is not made and power must be turned on again because this state is maintained.
• Protection of output overcurrent: When the total output current of three channels reaches approx. 3.95 A, the
main converter IC function is disabled and the 12 V output is shut off. At this time, the LED_ALERT signal
is output. Automatic reset is not made and power must be turned on again because this state is maintained.
• Protection of output short-circuit: When the output is short-circuited, the 12 V output is shut off by the
overcurrent detection function of the main converter IC. When the cause of the short-circuited has been cleared,
automatic reset is made and 12 V is output again.
3. Power output for alarm LED (LED_ALERT)
When the output overvoltage protection or output overcurrent protection function is activated, the 12 V output is
shut off. Power to turn on the alarm LED on the non-powered KY-687 board is supplied separately.
Output system:
• One channel to the KY-687 board
When the overvoltage protection or overcurrent protection function is working, the LED_ALERT signal is output.
The LED_ALERT signal is created by the 3-pin regulator for internal reference power voltage and the timer IC.
The output is a blinking signal of approx. 10 V/0.65 seconds and 0 V/0.33 seconds (max. 20 mA).
AVP-18 Board
The AVP-18 board consists of a power circuit and a power microcomputer (IC1202).
However, some low power voltages are contained on the DPR-340 board.
1. Operation of input power (UNREG) system
UNREG power is input and the AVP-18 board becomes the EVER power state.
In this state, ON or OFF of the power switch can be recognized.
When the power microcomputer (IC1202) recognizes ON of the power switch, the power microcomputer turns on
the system control power and controls power for each block in accordance with instructions of the system controller
(IC700).
The normal input power (UNREG) value is within a range of approx. +10.5 V to +18 V.
• Protection of input overvoltage:
When the UNREG power voltage is high, the overvoltage protection circuit is activated at the set value of
+17.9 V to shut down the input voltage. This circuit allows automatic restoration of power immediately when
the input voltage lowers to +17.9 V or less.
• Protection of input low voltage:
When the UNREG power voltage is low, the low-voltage protection circuit is activated approximately at the
set value of +10.5 V by the power microcomputer control to shut down the input voltage. When the input
power voltage rises to +10.5 V or more, power is immediately restored automatically by the power
microcomputer control.
• Detection of overcurrent:
The AVP-18 board is provided with an overcurrent detection circuit consisting of IC904. The set value is
approx. 4.3 A. Even if IC904 is reset after an overcurrent has been detected, automatic reset is not made and
power must be turned on again.
• Protection of reverse power connection:
If input voltage polarity is reversely connected, Q901 on the AVP-18 board is immediately turned off and the
GND side of the UNREG power is shut off to activate the protection function.
MCC-3000MT
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