Functional Overview - Covidien Valleylab LS10 Service Manual

Functional Overview

The Valleylab LS10, LS Series Single Channel Vessel Sealing Generator is a LigaSure vessel
sealing system. The LigaSure system provides power for vessel sealing. The LigaSure
vessel sealing system provides precise energy delivery and electrode pressure to vessels
for a controlled time period to achieve a complete and permanent fusion of the vessel
lumen.
RF Tank Circuitry
The primary purpose of the RF tank circuitry is to convert the +48 DC volts coming from
the commercial power supply into a 400kHz RF signal that is sent to the LigaSure
receptacle output. A full H-bridge topology drives the tank circuitry and is used to
accomplish this voltage conversion. The RF transformer that is a part of the tank circuitry
both steps up the voltage and provides isolation.
The four gate drive signals driving the H-bridge come from the DSP. A full cycle of the
H-bridge output is:
1) High on the "left" side, low on the "right" side
2) Dead time, high on both "left" and "right" side
3) Low on the "left" side, high on the "right" side
4) Dead time, low on both "left" and "right" side
This cycle repeats at a 400kHz rate. The two on times are identical in length and the two
off times are identical in length.
The power delivered to the LigaSure receptacle is changed by varying the ratio of the on
time to the off time. This ratio is referred to as the "phase" of the driving signals. The
phase varies between 10° and 160°. In order to keep both the FET devices on one side of
the H-bridge from being on at the same time, there is a minimum amount of dead time
guaranteed by the DSP.
Voltage and Current Sensing
There are two independent and identical voltage and current sensors. One voltage and
one current sensor feed the DSP and the other pair of sensors feed the Host processor.
The voltage and current sensors feeding the DSP are each digitized and read by the DSP.
Having both the voltage and the current allows the DSP to compute the power being
delivered to the tissue, the impedance of the tissue, and the phase between the voltage
and the current. The tissue impedance is used by the algorithms in the DSP to control the
power being delivered to the tissue.
The voltage and current sensors that feed the Host processor first go through an analog
multiplier The single output of the multiplier represents the power being delivered to the
tissue.
The voltage sensor is a highly accurate capacitor that couples the RF voltage into a filter.
The current sensor is a Rogowski coil that generates a voltage across a resistor. That
voltage is coupled into another filter. Each of the filters consists of a low pass filter, a
high pass filter, and an integrator.
Valleylab LS10, LS Series Single Channel Vessel Sealing Generator Service Manual
Functional Overview
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