Pulsar
2
Service Manual
OPTIKON 2000
Cod. 111004SEN Rev.C
5-17
Reference voltage Vb can be varied by the microprocessor by the means of
DAC U3. The information conveyed by micro to DAC U3 is determined by the
means of a patented electronic circuit named “Minimal Stress” (ESS module in
the schematics).
The U/S amplifier is stopped for 2ms 100 times per second: during the stop
period, the handpiece continues its oscillation because of mechanical inertia,
this oscillation excites the piezoelectric crystals, which generate a voltage
proportional to the amplitude of oscillation. This feedback voltage is compared
to the PRESET analog signal from the Control Board (which represents the
desired amplitude of oscillation set by the operator). The result of this
comparison is then used to set the voltage to the U/S amplifier for the next
cycle.
Phase-shift detector section
The sinusoidal voltage present on the handpiece, is squared and made TTL-
compatible by the U17 Zero-Crossing-Detector and sent to the PLD ( ZCR
signal).
It is then compared with signal CK40K coming from local oscillator U9, and its
phase-shift is measured. The phase-shift value is a 6-bit word ( Q0-Q5 signals
of PLD) and it is sent to buffer-latch U15, where it is available for reading by
the microprocessor.
Handpiece acknowledgement
The microprocessor can determine if the handpiece is connected to the
console by reading U7A comparator output. When handpiece is cut-out, the +
inlet of comparator is at high level. When handpiece is connected, the + inlet
goes to 0V since handpiece has an inside shunt to ground.
5.4.2 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.
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