RF Board
Principles of Operation
LigaSure Vessel Sealing Generator Service Manual
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Heat Sink
The heat sink dissipates heat generated by the T_ON\ switching of power FET
Q5. In the normal mounting configuration, the heat sink connects electrically and
mechanically to the secondary circuit protective earth-chassis ground.
IsoBloc Circuit
The IsoBloc circuit provides a means of detecting a switch closure in an output
accessory while maintaining electrical isolation between the generator output and
ground referenced circuitry. This circuit consists of the following components:
•
An isolated DC power supply
•
A comparator to detect switch closure
•
An optoisolator link from the output connected circuitry to the ground
referenced low voltage circuitry.
Each handswitching output of the generator is associated with its own IsoBloc
power source and isolated signal paths.
Isolated Power Supply
The isolated power supply uses a quasi-resonant flyback mode converter to
generate the voltages for operating the IsoBloc circuit. The power supply consists
of an oscillator, a resonant flyback transformer stage, and secondary half-wave
rectifiers.
The IC chip, U13, configuration is as an astable oscillator, ground referenced with
an operating frequency determined by R63, R81, and C91. The U13 output drives
the resonant flyback transformer stage through the ON/OFF switching of FET Q6.
In the flyback operating mode, resonance occurs because of the tuning created by
T8, T9, and C69. A result of the resonance, a half-sine flyback signal, exists on
the drain of Q6. T8 and T9 also transformer couple the half-sine flyback signal to
the RF generator, patient connective floating RF output. Components CR33,
CR36, C94, and C106 then provide the half-sine rectification and filtering to
generate the IsoBloc power supply voltages.
The system includes two isolated power supply voltage sources: +V_ISO_1 and
+V_ISO_2. These DC voltage sources route their supplies individually to each of
the seal and bipolar mode floating handswitch circuits.
Caution
The heat sink normally exists at ground potential, posing no safety hazard during
RF generator activation; however, take appropriate precautions when testing and
troubleshooting this area of the generator.
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