8
gbo Medizintechnik
AG 2009
Version 1.0
1.4.2 current amplifier
This board handles the generation of the current signals. It includes a seperate microcontroller. The
software running on this microcontroller can be updated by the operating Software, so there is no
need to open the device and install the software manually to this processor. The CPU controls the
frequency and the amplitude of the current signal, which is amplified in the power amplifier. The
power amplifier is based upon two power Mosfet transistors. A relay separates the patient from the
current signal.
The detection of an open circuit is also included on the board. The patient current is measured and
transfered to the operating software. The communication between operating software and the
current amplifier is performed by serial interface. In case of three channel treatment the current
amplifiers can be synchronized.
The supply voltage of ±200V are generated on each current amplifier board. The ±15V are
generated out of the +5V supply which are generated separetely for each channel at the bus board.
Sinus Signals are generated by a DDS Chip, multiplied with the Intensity and amplified by the
power stage. All other signals are generated by the Microcontroller, multiplied and amplified by the
power stage.
The power amplifier boards are directly plugged to the bus board by two connectors. A maximum
of three boards can be connected to the bus board. The boards are kept by card holders and secured
with safety sticks. 3 current amplifier boards are installed in Stereodynator. They are directly
connected to the connector board by a cable harness.
A relay for combination therapy allows to switch the current signal to the ultrasound amplifier.
However, combination therapy is only possible at channel II. The combination therapy relay
switches the electrode contact of channel II to the metal surface of the ultrasound probe.
1.4.3 Ultrasound
amplifier
This board handles the generation of the ultrasound signals. It includes a seperate microcontroller.
The software running on this microcontroller can be updated by the operating Software, so there is
no need to open the device and install the software manually to this processor. The CPU controls
the frequency and the amplitude of the ultrasound signal, which is amplified in two stages, a
preamplifier and a power amplifier. The power amplifier is based upon two power mosfet
transistors. A transformer insures the isolation of the patient.
A relay is used to switch between the two ultrasound outputs of this board. So only one of the ultrasound
outputs of the device will be active. It is possible to pass a stimulation current signal to the selected probe, so
that the electrical signal will appear at the surface of the ultrasound probe.
Another relay is used to switch an on-board filter circuit from 1 MHz to 3 MHz mode. The electrical signals
for the ultrasound probes are measured and used by the CPU for power regulation and coupling detection.
The power amplifier section may be switched off completely to protect it from overcurrent. A circuit senses
the current and reversibly switches the power amplifier stage’s power supply off completely.
The temperature of the heat-sinks directly fixed to the PCB is sensed by NTC sensors.
The US power amplifier generates 27V supply voltage from the 48V which comes from the power supply.
Also, -5V are generated as supply for the analog parts on board. The +5V supply is generated on the bus
board.
Communication is done by RS232 signals running to the bus board. This interface is also used for Software
updates.
The power amplifier board is connected by a 7 pole cable to the bus board.
