Panasonic KX-TDA6178 Service Manual page 17

24-port single line telephone extension card with caller id
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KX-TDA6178
• +80V/-30V/-55V Converter
For +40V input power supply, Q801 is switched ON with input voltage of 22V to start up input power supply. Q809 is switched
ON with input voltage of 28V to supply 15V to control circuits in all converters. Then all converters start up. Circuit configuration
of -30V/-25V converter is same as +80V. In event of an over current in the 40V input line, due to a short circuit in the MOSFET
Q804/Q805 switches, Q801 is cut off and the input power supply is shut down.
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