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HP 82713A
Theory of Operation
2-25.
Power Supply
2-26.
The Power Supply provides power to the PMS when it is not powered
by 1ts primary source, the HP-75. When the PMS is not plugged into the
HP-75, the Power Supply provides power to all of the circuits including
the RAM. This maintains the contents of RAM making the PMS self-sustaining
and portable.
2-27.
The heart of the Power Supply is the battery (BT1). It is
a single cell Lithium-Iodine type. It does not contain any liquid or gaseous
chemicals. It exibits very long shelf life as well as being hardened against
environmental extremes. It is enclosed in a laser sealed case. Its expected
life is in excess of 5 years.
2-28.
The Power Supply contains diode circuitry that automatically switches
in. Whenever the PMS is plugged into the HP-75, the VI line is held high.
This suppresses current flow through CR2 and essentially isolates the
battery from the circuitry. Whenever VI is not powered (PMS removed from the
HP-75), CR2 allows current from the battery to flow. The battery then
energizes all of the IC's and maintains the RAM.
Figure 2-10.
Power Supply
2-9
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