147 / 2663 CIRCUIT DESCRIPTION
Art. No.: 80116-201
09 / 2004
For example, if area 1 is activated, the emitter from transistor T2 is set high and gives its output voltage via
the trim potentiometer TP 11, resistor R45 and diode D2 to the measurement line U_NETZT, which also
leads at the power module to the sensor line of the switched-mode power supply's output voltage, but at the
same time also to the measurement system of the processor (trim potentiometer TP1 on the control board).
Transistor T2 can therefore be regarded as an extra-low voltage power supply, the output voltage of which
the HF generator of the power module uses to produce a minimal HF voltage and emit this as a test voltage
to the bipolar socket.
The internal impedance of this mini power supply unit is adjusted via the trim potentiometer TP11.
If the generator is now loaded with the tissue in the forceps (or with a 2.5 kOhm impedance), the supply
voltage at the internal impedance of the mini power supply unit collapses by a specific amount.
This voltage collapse is measured by the processor system and compared with the prescribed set values. If
they agree, the main power supply unit is switched on and the HF generator supplies the preset power.
The mini power supply unit cannot be fed in reverse due to the diode D2 (protective diode).
Since the internal impedance can be changed via the trim potentiometer TP11, the starting point of the
contact monitor can be adjusted here relative to the loaded impedance of the generator (tissue impendance).
Actuation and power setting of the ST output stage
The instruction to actuate the ST output stage arrives as a digital word from the control bus. From this, in
the digital-analog converter IC8, a DC voltage results which is transformed into a specific frequency in the
voltage frequency converter IC15, which can be adjusted using the trim potentiometer TP17.
The clock pulse generated in this way is the repetition frequency of the ST output stage actuation.
The pulse length of each individual actuation pulse is taken from the repetition frequency. Using the EXOR
of the IC12, a monoflop is realized with which the pulse length of the actuation pulse can be adjusted using
the trim potentiometer TP16. After a steepening of the edge, the actuation pulse TSI_STE is available at
output 11 of the EXOR IC12.
The generator power can be adjusted via the repetition frequency.
Actuation of the power module
The power generator of the power module is a feedback generator in principle which receives its actuation
pulse from the control board. The generator, however, does not begin to oscillate itself, but must instead be
started by a pulse.
The circuit receives the start-up signal and thus the necessary starting pulse from the processor via its PIO
on the CPU board and the transistor array IC8 on the motherboard.
The HF_EIN signal is directed to the comparator IC14 on the control board, the output of which remains at
logical HIGH during activation.
When starting up, the ascending signal is differentiated via the RC element R19, C73 and moves to the gate
of the transistor T4 which then briefly connects through and triggers the monoflop IC16. This is the starting
pulse at which the generator begins to operate. Using the trim potentiometer TP15, the pulse length of the
first monoflop in the IC16 can be set and resulting in a symmetrical sine-wave characteristic for the generator
signal (adaptation to the parallel oscillating circuit).
Control board
Slot J3
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