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four harmonic signals and generates the multi-tone audio alarm signal. Based on the input to the 2:1
multiplexer (U4) the multi-tone signal is fed to one speaker driver circuit at a time.
Audible Alarm Driver - The two audio alarm signals are fed to the respective piezo speaker drivers (U7 &
U11) via the summing amplifiers (U14 & U15). The piezo speaker drivers have integrated boost converters and
audio power amplifiers capable of driving the speaker load with a 16Vp-p signal. They provide pop-and-click
removal function through bypass capacitors (C17 & C49) which determine the turn-on time of the audio
amplifier. In addition, the speaker driver circuit provides the band switch function for a soft alarm sounding, and
low power shutdown to support low power mode.
Speaker Monitoring Circuit - The operation of each speaker is verified using the current monitors sub-circuit.
When a speaker is turned ON the high-side current shunt monitor (U8 & U12) generates an output current
proportional to the differential voltage generated across the current sense resistors (R27 & R59). The output
signal is used by the comparators (U9 & U17) to generate the alarm status signals for the CPU to verify
speaker operation. The reference voltage for the comparators (U9 & U17) is set at 193mV.
Speaker Circuit Power - There are two independent power sources available to power the two speaker
circuitry. The power mux (U13 & U16) select one of the two available power sources for each speaker circuitry.
Both the speaker circuits use the different power supplies as primary and backup supplies.
4.7 I
B
NTERFACE
The interface board provides the means for the Trilogy ventilator to communicate with external devices such as
the humidifier and other accessory devices. It includes circuitry for ethernet communication, RS-232 and RS-
485 communication, oxygen sensing, remote alarm interface and accessory power generation.
P
4-12
AGE
OARD
To
Isolation
System
Transformer
Board
Heater
Power
Source
Sensor
Power
Source
To
Isolation
System
Board
24 VDC
SUPPLY
485
Transreceiver
F
4-7 I
IGURE
NTERFACE
T
S
RILOGY
ERVICE
Ethernet
Oxygen
A
Sensor
Current
Sense
Accessory
RS-232
Humidifier
B
B
D
OARD
LOCK
IAGRAM
& T
I
ECHNICAL
NFORMATION
Nurse
Call
Device
1002735, V
. 05
ER
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