Power Supply/RF Board
4-26 Force FX Electrosurgical Generator C Service Manual
Bipolar Modes
The circuit topology for the bipolar modes is essentially the same as the cut modes,
except the output voltage is tapped off C152 and the switching frequency is 470 kHz.
These differences allow for the higher currents and lower voltages required in bipolar
surgery while still maintaining the advantages of zero voltage switching in the MOSFET.
The T_ON\ signal is a continuous pulse train with a 423 ns pulse width.
Coag Modes
In the Fulgurate and Spray coag modes, K2 is set so that diode CR2 blocks reverse current
in the power MOSFET, C40 as well as C34 and C41 are across the MOSFET, and the
transformer primary consists of winding 1-2 only. K14 is open, keeping the series
capacitor bank (C150–C152, C158, and C159) out of the circuit.
In the LCF Fulgurate coag mode, the T_ON\ signal is a continuous pulse train with a pulse
width of 1.69 µs and a repetition frequency of 57 kHz. When the MOSFET turns on,
some energy is delivered to the output and some is stored in the T4 core. When the
MOSFET is turned off, the energy stored in the core rings out with a frequency of
591 kHz.
The frequency is set by C34, C40, C41, and the inductance of winding 1-2 of T4. CR2
blocks reverse current in the body drain diode of the MOSFET so that the power
waveform can ring negative. This allows high peak voltages to be achieved at the output.
In most cases, all the energy stored in the transformer core during one switching cycle is
delivered to the load before the next cycle begins. The Fulgurate mode works the same
as the LCF Fulgurate mode, except the T_ON\ signal is a continuous pulse train with a
pulse width of 1.69 µs and a repetition frequency of 30 kHz.
The Spray mode works essentially the same as the Fulgurate mode, except the T_ON\
pulse frequency is randomized over the range of 21.6 kHz to 35.23 kHz. In addition,
amplifier U7A randomly varies the output amplitude by 10%. The ECON–GAIN signal
from the Control board changes the gain of U7A between 1 and 1.1.
To minimize rin gi ng on the outpu t vo ltage waveform at light loads, transistor Q7
switches in the 50 watt, 150 : heat sink mounted resistor in series with the transformer
primary for part of the RF switching cycle.
In the Desiccate coag mode, K2 is closed and K14 is open. The T_ON\ signal is a
continuous pulse train with a pulse width of 2 µs and a frequency of 39 kHz. The output
resonates with a frequency of 308 kHz.
Output Relays
In all monopolar modes, K13 is closed and routes patient return current through the
Patient Return Electrode receptacle. K15 routes active current through the Monopolar
1/CEM Instrument receptacle. K16 routes the active current through the Monopolar 2
Instrument receptacle.
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