Passport 2®/Passport 2 LT™ Service Manual 0070-10-0441 2 - 35
Theory of Operation XE-50 Recorder Interface Board
2.9.5 5V Regulator (U4)
The 5V Regulator circuit, comprised of the Micrel MIC2954 three terminal regulator, which
derives +5V from the incoming +12V (+12V2). The regulated +5V is referenced to the 12V-
return in order to minimize the introduction motor noise generated by the fan.
Q2, Q3 and Q5 isolate the boundary between the CPU Module's circuit ground potential,
and the local ground potential. Since the two are referenced to different supply voltages,
they can be significantly different.
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