uniphy Phyaction 740 Series, Service Information

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Service Information Phyaction 740 & 790-series Page 19
Settings of parameters as duty cycle, treatment time and frequency, 1 or 3 MHz resp., is done over the
user interface. The microcontroller determines the precise operating frequency for the selected treatment
head, based upon the identification codes that have been entered during installation of this treatment
head. These codes are also used to assess the emitted amount of ultrasound power. The microcontroller
also counts down the treatment timer, which it will halt when the emission of ultrasound power is
interrupted during the treatment. The operator sets the required ultrasound intensity with the control-knob
of the same name. The microcontroller uses the control-voltage
V
potus
together with the identifying codes
and the type of the selected treatment head to calculate V
control
which is fed to the SSMPS in order to
generate the requested amount of ultrasound power. The momentary output power converted by the
duty cycle is shown on the display as effective output power.
2.4.1 PLL
Because the microcontroller is not capable of generating the drive frequency directly, a PLL (Phased
Locked Loop) is used to convert the low-frequency control-signal
f
control
to the drive frequency
2x
f
us
needed. Like the description suggests, this frequency is a twofold of the ultrasound-frequency because it
gets divided by two in the modulator. As there are two operating areas for the ultrasound-frequency,
about 0.8 and 3.3 MHz respectively, and the control-signal
f
control
always is lying about 400 Hz, the
feedback loop of the PLL is closed via a divider whose divisor is switched together with the oscillator
range. To prevent operation on faulty ultrasound-frequencies, e.g. in absence of the
f
control
signal, a lock-
out monitor has been provided whose output is wired-orred with Error
us
.
2.4.2 Modulator
The modulator switches its outputs with half the rate of the drive frequency
2x
f
us
to achieve an exactly
symmetrical driving of the power stage. The duty cycle signal is used to switch off synchronously both
outputs in order to prevent any 'misfirings'. As a result the ultrasound output-signal is completely switched
on and off (CW modulation).
Error
us
forms another way to switch off the outputs asynchronously in case
of a fault.
Figure 3, Functional blocks of the ultrasound therapy unit