HP 70427A User Manual page 508

NOTE
NOTE
Controller, I/O Interface and Power Supply Assembly A6
The I/O interface also multiplexes between and measures the analog voltages
returned through the diagnostic multiplexer system. This system provides
the voltage measurements needed for power and frequency setting, and
allows for module trouble shooting and monitoring without disassembling
the module. The DC voltmeter has 12-bit resolution, and has an input range
of ±10 V. AC measurements of the diagnostic multiplexer system are
possible through the buffered output on the rear panel of the module. The
bandwidth of the rear-panel output is DC to 100 kHz.
Power Supply
The power supply provides six regulated low-noise output voltages, and two
unregulated voltages. The regulated outputs are ±5 V, ±10 V and ±15 V. The
unregulated supplies are +25 V and +50 V.
The input voltage to the supply is 24.3 V AVG ±1% at 40 kHz.
24.3 V AVG is approximately 27 V
about 90 watts, drawn by an HP 70428A Option 002 at 26.5 GHz.
The power supply's input is fused by two 2.5 amp fast-blow fuses, one fuse
for each of the 40 kHz power transformers.
The fuses must be removed from their pin socket holders to be tested.
The power supply input circuitry is designed to minimize 40 kHz radiation
into the rest of the module. The transformer inputs are isolated from the
MMS mainframe's 40 kHz switching supply by two bifiler wound isolation
chokes. All 40 kHz signals on the PCB are routed using co-plainer
transmission lines to minimize 40 kHz radiation induced spurs. The
transformers are also built with a 40 kHz hum shield to reduce spurs.
Inductors in the power supply are built either as pot core inductors or toroid
inductors, both of which are self-shielding.
The voltage reference for all of the regulated supply output is produced by a
precision +10 V monolithic voltage reference (U101) which is adjusted, by
R165, to +10.0 V, ±0.002 V. The output noise of the +10 V reference is about
100 nV/Hz. The reference output is followed by a 0.3 Hz noise filter which
reduces the reference noise to less then 10 nV/Hz at 3 Hz. During power-up,
the noise filter is bypassed by back to back silicon diodes (CR101 & CR102)
which allow the power supplies to rise to 90% of their final value very
quickly, and then drift into the final value over the next 30 seconds. The
noise filter output is buffered by an OP-77 op-amp (U102) which provides
the current necessary to provide voltage reference for the negative power
supplies. The +10 V reference is inverted by a second OP-77 (U109) to
produce the –10 V reference which drives the positive regulated supplies.
. The worst cast power dissipation is
rms
HP 70427A/HP 70428A User's Guide 13-73
Block Diagram