Utah Medical Products Finesse ESU-110, Service Manual

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C
I R C U I T
D
E S C R I P T I O N S
Note: Schematics for the Finesse ® generator will be made available
on request to qualified technical personnel.
Power Supply
The power supply for all electronic functions is derived from the
input line supply through a multi-winding transformer mounted on
the floor of the unit. Circuits are conventional, non-switching sup-
plies using bridge rectifiers, electrolytic filter capacitors, and series
regulators. Except for the line connections, transformer, and fuses, all
DC power supply components are mounted on the power supply
board (see functional diagram on page 28 and assembly diagram on
page 24).
The 200 volt supply furnishes power to the preamplifier and final
output stages. This supply is not actively regulated; however the
volt-amp capacity of the transformer itself is sufficient to maintain
sufficient voltage under load to provide the set cutting or coag out-
put, and the preamplifier and output stages are feedback regulated at
the RF level so that the variation in cutting output over a large
change in supply line voltage is small.
The 30 volt regulated DC supply begins with a 28 volt rms secondary
winding on the main power transformer winding. A bridge rectifier
with a capacitor input filter converts this to approximately 40 volts
DC for use by both the 30 volt and 15 volt regulators. The 30 volt
regulator is a three terminal linear regulator.
The 15 volt regulated DC supply for powering the CMOS logic chips
also uses the 40 volt bridge with a three terminal linear regulator. A
resistor between the regulator and the 40 volt unregulated supply
protects it from excessive current in the event of a shorted compo-
nent.
The five volt regulated supply furnishes power to the LED display
devices on the display board. A 5 volt regulator chip is fed from a
separate winding on the main power transformer.
Output Level Control and Display
The cut/blend and coag modes of operation are separately controlled
with parallel circuitry. However, only the operation of the cut/blend
control circuit will be described.
The desired output for cutting is set by turning the cut/blend output
control knob on the front panel until the digital output indicator dis-
plays the correct value. Voltage from the front panel potentiometer
is routed to the A-D input on the digital display board. R3 in this
path is provided to set the display to read "99" at the fully clockwise
setting of the front panel knob.
The A-D converter converts the adjusted voltage at this point to a
digital value which can be manipulated by the main display proces-
sor. A linearization curve is programmed in the processor for each of
the cut and three blend modes so that the proper output control
level is presented digitally to the D-A converter at any setting from
the front panel.
The D-A converter translates the output of the processor to an analog
voltage which, after some additional scaling, will act as drive to the
power generation circuits. Two potentiometers on the logic board
allow for offset and gain adjustment of this voltage. A summing
amplifier at the output of the D-A converter provides a means for
amplifying, attenuating, or offsetting the control voltage and, also,
provides a mixing point for subtraction of the voltage signal fed back
from the generator output.
The adjusted output voltage, mixed with the feedback signal, is rout-
ed to individual variable-gain buffer amplifiers that are provided for
setting the drive levels of each mode in final calibration. The outputs
of these power level control amplifiers are connected to a bank of
transistor switches which act to select the proper voltage for each
selected mode of operation and present it to the DC-AC converter.
These transistor switches are logically controlled by signals from the
mode switch on the front panel and by the cut/blend and coag acti-
vation signals from the power board.
The DC-AC converter is a FET chopper whose drain voltage is the
conditioned output control DC voltage and whose gate is driven
Finesse Service Manual
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