Covidien Force FX, Руководство по обслуживанию

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Power Supply/RF Board
4-24
Force FX Electrosurgical Generator C Service Manual
Cut Modes
In the cut modes, K2 is set so that diode CR2 is in parallel with the MOSFET body drain
diode, C34 and C41 are across the MOSFET, and the transformer primary consists of
windings 1-2 and 3-4 in series. K14 is closed so the series capacitor bank (C150–C152,
C158, and C159) is across the output.
In the Low and Pure cut modes, the T_ON\ signal is a continuous pulse train with a pulse
width of 846 ns and a frequency of 390 kHz. In this case, essentially two resonant circuits
operate in tandem.
The output L-C filter is tuned just slightly higher than the RF switching frequency,
achieving a high degree of filtering. The output is very sinusoidal over the full range of
load impedances.
Capacitors C34 and C41 are tuned with the RF transformer primary so that the flyback
voltage appearing across the MOSFET at turn off is a half sine pulse and returns to zero
volts before the next cycle begins. The T_ON\ pulse width is chosen to support this
tuning. This zero voltage switching improves the efficiency of the RF stage and is effective
over a wide range of load impedances.
The circuit topology of the Blend cut mode is the same as the Pure cut mode. In Blend
mode, however, the T_ON\ signal is an interrupted pulse train with a 50% duty cycle and
a pulse train repetition rate of 27 kHz.
For a given power setting, Blend gives a higher peak current, providing better hemostasis
than Pure or Low. To minimize ringing at the beginning of the off period of the Blend
waveform envelope, the damping resistor is switched on just before switching ends and
stays on for part of the off period.
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.