Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual
10070389 Rev. A
2-43
2.3.1.2 Power supply
See Figure 2-29. The power supply outputs a constant reg24 V DC. It accepts input
voltages in the ranges 85 to 134 V (110 V units) or 171 to 269 V (230 V units) at 45 to 65 Hz.
The power supply has a single, +24 V output, which is fused on the BBU PCB. It provides
power for ventilation and battery charging. Voltages required by the PCBs are generated
locally from the distr24 V.
The power supply is protected against overvoltage, overtemperature, overload, and load
short circuit conditions.
Figure 2-29. Power supply with harnesses
2.3.1.3 Battery backup (BBU) PCB
Figure 2-30 and Figure 2-31 illustrate the battery backup (BBU) PCB, which contains the
circuitry needed to switch between available power sources, power the motor, and charge
the internal and external batteries. It also monitors various supply voltages as well as the
power assembly temperature.
• The
battery backup circuit
determines whether the AC source/power supply can provide a
re24 V output for ventilator operations. If the circuit determines it cannot, then
the circuit switches to external or internal battery as the power source. (For a complete
description of the power source switchover operation, see Section 2.7.) This circuit
operates independently of both microprocessors, although the UI microprocessor does
test the batteries, monitor the battery backup circuit, and switch off battery power when
the powering battery output falls below 21 V.
• To determine which power source to use, the battery backup circuit monitors the
three +24 V outputs from the power supply, external battery, and internal battery.
Normal ventilation can proceed if one of these outputs is at least +21 V. The
ventilator’s first choice is to operate from the power supply output (powered off
the mains), then the external battery, and then the internal battery. Before
operating from the power supply, however, the circuit verifies the power supply
output is stable and remains stable for three seconds. For the first three seconds
after the ventilator power is turned on, the ventilator is powered by the external
(if available and charged) or internal battery. After three seconds, provided the
power supply output is determined to be acceptable, the ventilator switches from
operating from the battery to operating from the power supply.
• If none of the three power sources is acceptable, the ventilator attempts an
orderly shutdown of the ventilator circuits.
To power
output
To power
input
Summary of Contents for Puritan Bennett 700 Series
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