Power Supply Theory; A15 Preregulator - HP 8753D Option 011 Service Manual

sampler is also related since it is part of the source phase lock loop. The source supplies a
phase-locked RF signal to the device under test.
The signal separation group divides the source signal into a reference
Signal Separation.
path and a test path, and provides connections to the device under test. To accomplish
this, one of several external test sets must be connected to the analyzer.
The receiver group consists of the A4/A5/A6 sampler/mixers and the A10 digital
Receiver.
IF. The A12 reference assembly and the A9 CPU are also related. The receiver measures
and processes input signals for display.
The following pages describe the operation of each of the functional groups.

Power Supply Theory

The power supply functional group consists of the A15 preregulator and the A8 post
regulator. These two assemblies comprise a switching power supply that provides regulated
DC voltages to power all assemblies in the analyzer. The A15 preregulator is enclosed in
a casting at the rear of the instrument behind the display. It is connected to the A8 post
regulator by a wire bus A15W1. Figure 12-2 is a simpli ed block diagram of the power supply
group.
Figure PSBLK12 here.
Figure 12-2. Power Supply Functional Group, Simplified Block iagram

A15 Preregulator

The A15 preregulator steps down and recti es the line voltage. It provides a fully regulated
+5 V digital supply, and several preregulated voltages that go to the A8 post regulator
assembly for additional regulation.
The A15 preregulator assembly includes the line power module, a 60 k z switching
preregulator, and overvoltage protection for the +5 V digital supply. It provides LEDs, visible
from the rear of the instrument, to indicate either normal or shutdown status.
12-4 Theory of Operation
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