Low Voltage Power Supply
Principles of Operation
LigaSure Vessel Sealing Generator Service Manual 5-17
Thermal Sensing (High Temperature Limit)
A reference voltage determined by R9 and R11 goes to the non-inverting input of
comparator U3B. High temperature limit control occurs when the temperature of
the NTC thermistor R22 reaches approximately 65° C, which causes the inverting
input of comparator U3B to drop below the reference voltage and trip the
TEMP_HI signal. Resistor R10 provides positive feedback causing approximately
10° C of hysteresis between heating and cooling thermal sense activation.
When the main microcontroller reads the TEMP_HI signal, it flashes number 451
alternately with the power settings. This disables the generator and prohibits any
RF output from occurring. When the temperature drops to approximately 55° C,
the circuit reverts to its low temperature state, and normal operation resumes.
Low Voltage Power Supply
The low voltage power supply is a medical grade triple output supply rated for 40
watts. It delivers a regulated +5 Vdc and ±12 Vdc output with current limit and
overvoltage protection. This power supply incorporates universal mains switching
which automatically adjusts for both 120 Vac and 240 Vac input voltage ranges.
The low voltage power supply provides low voltage power to the RF board at
connector J7. The following table shows the J7 connector pinouts:
The low voltage power supply specifications are as follows:
* Total output power cannot exceed 40 W.
PIN Voltage Test Point
1+5 VdcTP4
2–12 VdcTP3
3+12 VdcTP2
4 GROUND TP1
Output Voltage Output Current Output Power*
+5 Vdc 4000 mA 20.0 W
–12 Vdc 400 mA 4.8 W
+12 Vdc 2000 mA 24.0 W
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