Display Board
Principles of Operation
LigaSure Vessel Sealing Generator Service Manual
5
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11
Q1 through Q4 MOSFETS turn the RF indicator lamps on and off. Resistors R4,
R5, R9, R10, R13, and R14 set the amount of current flowing through the lamps
when they are turned on. The value of these resistors varies for each indicator bar,
depending on the color of the bar, to make the different colors of the bars
illuminate with equal intensities.
LED and Seven-Segment Display Drivers
This circuit contains two display drivers: the LEDs and the seven-segment
displays. The bar lamp LEDs indicate the seal intensity. The seven-segment
displays indicate the bipolar and macrobipolar power settings.
Each display driver (U10 and U11) can drive up to eight banks of eight LEDs by
multiplexing the time at which it turns on each bank and controlling how long the
bank remains on. Wiring the banks together increases the time that a group of
LEDs can remain on, effectively increasing the brightness of that group.
U10 drives the discrete bicolor LEDs. These include the red and green indicators
for the smart connectors in the bipolar and seal modes. The anode of each mode
selection LED connects to driver U10. Using pairs of the driver digit lines makes
the effective duty ratio for these LEDs 1/4.
U11 drives the seven-segment displays that indicate power settings. U5 and U6
indicate the bipolar power setting; U2 and U3 indicate the macrobipolar power
setting; and U1, U4, U7, U8, and U9 indicate the seal intensity bar lamp setting.
Seal bar lamp U12 illuminates yellow when you turn the power on and the system
completes its self-diagnostic test successfully. The yellow lamp setting
corresponds to a default seal power setting of zero output. The anodes of these
displays each connect to only one digit line of the driver. The effective duty cycle
is 1/8 for each seven-segment display.
Some filtering components are associated with U10 and U11. Bypass capacitors
C3, C4, C5, C6, C8, and C9 connect b 5V and DGND. C3, C5, C6, and
C8 have a relatively small capacitance value (0.1 µF or less) to filter higher
frequency noise. C4 and C9 have a relatively large capacitance value of 47 µF to
supply the large spikes of current for the LEDs generated by the multiplexing
action of the drivers, which typically occurs at 250 Hz.
Resistor components R16 through R22 and R31 reduce the input impedance of the
display driver inputs as seen by the main microcontroller on the control board.
This rounds off the edges of these digital signals, reducing high frequency
emissions. The lower impedance also reduces the susceptibility of the circuit to
noise from other circuits.
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