Theory of operation
2-44
10070389 Rev. A
Puritan Bennett™ 700 Series Ventilator System Service Manual
• The
motor drive circuit
includes power MOS FETs in a bridge configuration to drive the
brushless DC motor. It limits current to the motor to prevent excessive patient wye
pressure. It works in conjunction with the motor controller circuit (on the controller PCB)
and the motor/encoder to provide the velocity and torque profiles capable of delivering
the full range of ventilator flows and pressures. See Section 2.5 for a discussion of the
motor control and drive operation.
• The
battery charger circuit
charges the internal and external batteries while the ventilator
is operating on AC power with the power switch on. This circuit monitors the charging
current of both batteries and the discharging current of the battery currently in use. If the
battery voltage drops below +25 V, the charger boosts the charging voltage to +29.4 V
(
±
20%). The battery pack’s float voltage is +27.4 V (
±
20%); this float voltage charging
level decreases with increasing battery compartment temperature.
• Inputs from the
voltage and temperature monitor
allow the controller PCB to monitor the
two battery voltages, the power supply voltage, and local DC voltages, as well as the
power assembly temperature. The ventilator’s UI shows the charge level of the internal
battery.
• Replaceable
fuses
on the PCB protect these lines:
– Input from power supply (F6) (15 A, standard, T-type)
– Motor drive (F1) (10 A, fast-blow, F-type)
In addition, the PCB has several nonreplaceable thermal fuses that stop conducting when
current exceeds their rating, but which begin conducting again after they cool and
current returns to acceptable levels.
•
LEDs
on the PCB permit monitoring of these lines; they can be viewed when the power
assembly is partially disassembled:
– Power source inputs to PCB – Power supply (MAIN ON), external battery (EXT ON), and
internal battery (INT ON)
– Main +24 V power from selected source (+24V MAIN)
Figure 2-30. BBU PCB
7-00151
MAIN ON
LED
INT ON
LED
EXT ON
LED
Motor drive
fuse (10 A)
(F1)
Motor drive
LED
+24V MAIN
LED
Power supply
input fuse (15 A)
(F6)
Summary of Contents for Puritan Bennett 700 Series
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