Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual
10070389 Rev. A
2-77
2.7 Power source switchover
The 700 Series Ventilator System normally operates from AC (mains) power, but it switches to
battery operation if necessary. (See Figure 2-63). The ventilator switches to battery operation
in these instances:
• The +24V power supply output is <21 V.
• At power on (The ventilator operates from battery for the first three seconds, before
switching to AC).
The battery backup circuit on the BBU PCB monitors the +24 V power supply output and the
internal and external battery outputs. 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, 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. This means that for the first three seconds after the ventilator power is turned on,
the ventilator is powered from 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 AC power is restored after the ventilator has switched to battery, the ventilator again
verifies the power supply output is stable for three seconds before resuming AC power
operation.
If none of the three power sources is acceptable, the battery monitoring circuit on the BBU
PCB signals the controller PCB, which attempts an orderly shutdown of the ventilator circuits.
Various ventilator circuits are initialized (put into known states. Because critical ventilator
data is stored in NVRAM, which has its own battery, this data is not lost.) The ventilator
invokes the safety valve (SVO) open state (see next subsection). When the batteries are being
charged, the ON AC/BATTERY CHARGING LED is lit. When the ventilator is operating from the
battery power, the ON INTERNAL BATTERY or ON EXTERNAL BATTERY LED flashes.
Summary of Contents for Puritan Bennett 700 Series
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