Assistant Service Manual
OPTIKON 2000
Code 121008S 6-18 Rev. D
Diathermy driver section (Sheet 2/2)
Bipolar diathermy driver generates a voltage of an approximately sinusoidal
form, at a fixed frequency of 2 MHz. The maximum output power is 7W on
450 Ohm load. The output of diathermy if floating (insulated from any other
voltage or ground), current can flow only between the two opposite poles.
A free-running oscillator made up by U8A,R61,L4,C50 and C51 generates a
TTL square wave at the frequency of approx. 2MHz.
U8B is used as an inverting port to generate a second square wave of
opposite phase.
U8C and U8D are used as gates to apply the two square waves to the
MC3452 (U16) MOSFET driver only when the control signal ENDIA, from the
microprocessor, is low (0 Vdc).
Two power MOSFET, Q4 and Q5, are operated by the MC3452 driver, their
drain is connected to the primary winding of L5 which provides insulation
from the part applied to the patient.
The amplitude of oscillation can be changed (from 0 to 7 Watt) by changing
the control voltage at the central tap of L5. The adjustable power supply
circuit is the same used for U/S section (see previous description of
amplitude control section).
Output stage consists of R63 and R64 resistors that discharge circuit
capacitance, from C55 and C56 low frequency (heart hazardous) blocking
capacitors and from low-pass pi filters consisting of C53, L6, R73, R72.
Bipolar forceps or other accessories for bipolar diathermy are connected to
J4 connector.
Safety circuit
A simple Safety circuitry allows to the Control board to check if the 347888 is
generating a Diathermy or Ultrasound output (U/S_SIG and DIA_SIG) and to
measure the voltage level generated by the power supply module of the
board (U/S&DIA_PWR).
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