Power Supply/RF Board
Principles of Operation
Force FX Electrosurgical Generator C Service Manual
4-27
provide a return path for high frequency RF signals through C157 to the RF output
transformer. The REM transformer (T10) and capacitors C155, C156, C169, and C170
form a resonant circuit with a nominal operating frequency of 80 kHz.
Pin 1 of T10 clocks the active synchronous rectifier formed by CMOS switch U28A. This
device is closed during the positive period of the REM_AC signal and open during the
negative period. When the switch is closed, C122 is charged to the peak positive value of
REM_AC. Then, U31B amplifies, filters and buffers the charge on C122 to produce the
R_SEN signal. The microcontrollers monitor the R_SEN signal (which is a DC voltage
proportional to impedance) to determine the patient return electrode status.
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.
The IsoBloc circuit consists of an isolated DC power supply, a comparator to detect switch
closure, and 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.
Oscillator
The oscillator circuit consists of a chain of 74HC14 inverters. The output of the oscillator
yields a 67.5 kHz square wave that is applied to the input of three 4081 buffers (U29).
Power Supply
The three 4081 buffers (U29) drive three TN2404KL FETs connected to transformers
which are operated in a quasi-resonant flyback mode with their associated 6800 pF
capacitors. The voltages at the secondaries of the three transformers are half-wave
rectified and referenced to three separate isolated grounds to provide -8 V for operating
the isolated activation circuitry.
Optoisolators
The isolated power supply voltages produced by the IsoBloc power supplies are
connected to the active output terminals of the generator. Handswitch activation is
accomplished by sensing active to CUT or active to COAG switch closure in a handheld
accessory.
Switch closure is detected by comparing the voltage across the switch to a divider
reference with comparators U32, U33, and U34. Current through the limiting resistors, in
series with the LEDs in the optoisolators, cause the LEDs to light. The phototransistor in
the optoisolator detects this light.
Summary of Contents for Force FX
Page 1: ...Service Manual Force FX TM Electrosurgical Generator C...
Page 30: ......
Page 180: ......
Page 210: ......
Page 246: ......