Datascope Passport 2, Руководство по обслуживанию

Страница: 46 / 155

Power Supply Theory of Operation
2 - 36 0070-10-0441 Passport 2®/Passport 2 LT™ Service Manual
2.10 Power Supply
2.10.1 Part Numbers 0014-00-0250 and 0014-00-0190-01
The isolated power supply takes a raw +12V2 DC supply voltage and generates the
operating voltages required by the Front End Module. Since the input voltage varies over a
+/-5% range, some form of regulation is required. To preserve efficiency, a modular
switching supply is used.
This power supply requires sufficient isolation between the input and output to withstand the
open circuit voltage of a defibrillator, up to 5 KV. Further, it requires low capacitance
between the input and output, to minimize leakage currents which may flow should the
patient accidently contact line voltage.
Operating power is to be derived from the partially reg12V2 supply (4.0 W max.,
including the SpO2 module interface), and output as +5.5V and -11V. Several voltages will
be generated locally on the isolated front end, inc2.5V, +3.3VD, +5V, -5V, and +5P.
Other voltages will be generated on the SpO2 interface board.
The +5.5V and -11V DC output voltages vary according to load. The major source of load
variation is the presence or absence of the invasive pressure transducers. Certain portions of
the system, such as the A/D converter, and devices interfaced to the microcontroller require a
well-reg5 volt supply. This is obtained from the +5.5V rail by a linear regulator,
U802, whose enable line is activated immediately upon power up. A dedicated voltage
reference device, U801, is used as the +2.5V reference voltage for the A/D converter and
other parts in the frontend. The tolerance of this regulator (0.1%) is fairly good. In the case of
the invasive pressure, the transducer excitation voltage must track the +2.5V supply.
However, because the transducer circuits are prone to being shorted (as by spilling saline
into a connector), it is not advisable to directly use the +5 volt supply to excite the
transducers. Therefore, a second power source, a very accurate voltage regulator (1.0%),
U228, has been added for the pressure excitation. A voltage comparison is performed by
U223A, and output as EXSTAT. A compensation network consisting of C289, R323, and
R957 is used. In the event that the pressure excitation should be shorted out or overloaded,
U228 will go into current limit or shutdown, disabling the IBP function, but the +5 volt supply
from U802 will not be affected, so other functions will continue to operate. The +3.3VD used
for the microcontroller power is supplied by U805, a high efficiency step down switching
power supply. The power is created from the unreg5.5V, and a soft start feature is
implemented to aid the microprocessor to power up smoothly. There is no enable capability
for the +3.3VD, since the microcontroller must be powered up once power is applied to the
front end. The -5V used in the patient analog section is supplied by a linear regulator, U803,
whose enable line is activated immediately upon power up.
Power being supplied to the SpO2 modules is created on the SpO
2
interface board from
+5.5V and -11V, in order to eliminate any negative interaction resulting from shared
regulated power.