Pulsar
2
Service Manual
OPTIKON 2000
Cod. 111004SEN Rev.C
5-16
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).
Amplitude control section and Minimal Stress circuitry
Amplitude of sinusoidal signal applied to handpiece is proportional to the
direct voltage present at the central tap of primary winding of L1 transformer.
It is the output of switching regulator made up by U18,CR2,L2,C4.
This voltage, divided by R6,R7,R8, is applied to the NON INV pin of U7B (lets
call it Va) and compared with the reference voltage, set by the
microcontroller, present at the INV. pin (Vb).
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