Panasonic BT-M1950Y Service Manual page 115

Overcurrent protection
B1 malfunction
In event of voltage circuit malfunction causing abnormal 81 current, the horizontal oscillation is stopped.
Abnormally large
B1
current (twice normal,
1.0 - 1.2 A)
switches
0008
on. The collector goes High and switches on
deflection PB ASS'Y zener diode D706. The deflection PB ASS'Y IC501 pin 16 then goes High. Pin 16 is the Xray
protector terminal and when the input voltage exceeds 0.7 V, horizontal oscillation is stopped.
0019
~
Q008
OVER CURRENT PROTECTOR
~--------ff¥_.''
POWER PB
---i
~ DEFLECTION PB
0706
"""'~H---+
-·H
J4
.,,,
Fig. 2-4 Overcurrent protector circuit
Abnormal 0004 drain current
In event of damage to the above circuit system, rise in the primary side FET drain current is detected and the
switching power supply oscillation is stopped (see Fig. 2-2).
The drain current is converted into DC and applied to IC001 pin 5. When the DC voltage exceeds 0.6 V, the
pulse duty is increased to suppress the drain current, thus providing a current limiter function.
At the same time, C022 at pin 6 begins charging. If the excess current state continues intermittently, C022
continues charging. When the pin voltage reaches 2.2 V (typical), the pin 9 output is latched to provide an
overcurrent cutoff function.
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