Assistant Service Manual
OPTIKON 2000
Code 121008S 6-16 Rev. D
U/S Amplifier Section
The sinusoidal voltage supplied to the handpiece is picked up at the
secondary winding of L1 transformer and filtered through L3 and C9.
L1 primary winding is the load of the U/S amplifier, consisting of the two
power MOSFET (Q2 and Q3), operated by the U5 driver.
The CR3, C66 and CR4, C69 components limit the peak voltage upon
switching. The signals controlling the MOSFET U5 driver are two square
waves of opposite phase picked up from PLD ( Programmable Logic Device)
U10 ( DRV1 and DRV2 signals).
They are generated in the PLD starting from the 40 KHz ( CK40K signal)
clock signal originated by the VCO section.
Voltage Controlled Oscillator
Local oscillator consists of the U9 VCO (Voltage Controlled Oscillator). It
converts direct voltage available at the Vin input pin into a square wave at
the Fout output pin, the frequency of which is proportional to Vin. As Vin is
varied within an adequate range, an Fout signal can be produced, with
frequency variable in a desired range (in our case 37.5 to 43 KHz).
The circuit that generates Vin was designed in order to create a voltage
according to the following formula:
Vin (n) = V1 + n*V2
255
where n is an 8-bit-word provided by the microprocessor, that can take
values ranging from 0 to 255, V1 and V2 are two direct-voltage levels.
Therefore, Vin may vary between the values Vin_min = Vin(0)=V1 and
Vin_max=Vin(255)=V1+V2.
Voltages V1 and V2 call for an accurate calibration, as they determine the
tuning range.
V1 is determined by the trimmer R30 connected to U13B non-inverting
amplifier, whereas V2 is defined by R28, in the chain formed by the U12A
buffer, the U4 DAC (Digital-to-Analog Converter), the U13A non-inverting
amplifier.
The U13A and U13B non-inverting amplifiers amplify the reference voltage
supplied by the VR1 precision Zener diode (2.5 Vdc).
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