4-44 120 Series Maternal/Fetal Monitor Revision B
2015590-001
Theory of Operation: System Power Supply
System Power Supply
NOTE: The 2005845-001 power supply, found on newer builds, replaces earlier
13836 versions. The newer version has a higher current output on the +5V
line.
The power supply module in the 120 Series Monitor is manufactured by Power
Controls, Inc. The following technical information is a summary of the power
supply circuitry. This information is provided to give the hospital biomedical
engineer an overall summary of the power supply’s functions in relation to the 120
Series Monitor—to assist in isolating troubleshooting problems to the board level.
This information is not intended to provide a complete circuit theory and should not
be used to repair any problems on the board. When a problem does exist on the
board, contact your GE Service Representative for information about repair/
exchange of the power supply assembly.
The power supply is an off-line high-frequency switching power supply designed to
provide multiple regulated DC outputs from an AC source of supply. (The power
supply assembly is manufactured by Power Controls, Inc.)
The power supply incorporates direct rectification and filtering of the mains voltage
after fusing, in-rush limiting, and noise filtering are accomplished. An external
selector switch is provided to choose between 120 V or 240 V operation. The input
AC voltage need not be sinusoidal since no line frequency magnetic devices or
sensing circuits are employed. Input connection is made via an IEC-style discrete
line cord to allow adaptability to location of use.
The main DC output of 20 V is generated by high-frequency switching conversion
in the current mode controlled forward converter method of operation. The
frequency of operation is 72 kHz to which all post regulators are slaved and which is
synchronized to the system clock. All outputs other than 20 V are derived using
individual linear or buck type regulators to achieve voltage regulation current
limiting and short circuit protection. Over-voltage protection is by transient voltage
protectors on each output.
An exhaust fan is provided to move air through the entire system and out of the
enclosure at the power supply.
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