Revision C 170 Series Monitor 5-33
2000947-004
Theory of Operation: Main Board Theory of Operation
Power Supplies
Integrated circuit U60 is a voltage comparator that senses that the power has been
removed, and inhibits battery RAM access and recorder printing when the supply
drops to approximately 10 V.
Integrated circuit U58 forms an R-S flip-flop. U58 (pin 6) is set high when the
Power button is pressed. Q19 collector also goes to a logic 1 whenever the Power
button is pressed. When U58 (pin 6) is pulled high, it enables the SYNC signal at
U59 (pin 4) which is inverted by U59 (pin 3) to reach all the switching power
supplies. The sync frequency is 575 kHz and is derived, and hence synchronized to
the ultrasound system. U62 and its associated components comprise a buck
converter with an output voltage of +5.8 V. This is used as the pre-regulator for
linear regulators U65, U66, U68, and U69. U65 provides the system +5 V. U66
provides the +5 V for the recorder motor. U67 provides the +5 V for the audio
amplifier. U68 provides +3.3 V for the analog circuitry. U69 provides the +3.3 V for
the digital circuitry. U61, and its associated components, comprise a linear regulator
with an output voltage of +7.5 V. This is used as the pre-regulator for the linear
regulator U55 which provides the +6 V for the ultrasound front end; it also powers
U53 which provides the –6 V and powers U56 which is used to generate the +4 V
for the tocotransducer circuitry. U64, and its associated components, comprise a
boost converter with an output voltage of +24 V.
Integrated circuit U70, under microprocessor control, is used to control the +24 V
for the recorder printhead. The +24 V output is current limited by Q20, Q21, and
associated components. The power output is limited to 17 W.
Figure 5-20 provides a block diagram of the power supply section.
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