HP 13255 Technical Information page 11

13255
Power Supply Module
13255-91142/09
Rev SEP-06-77
3.1.4
Choke Input Power Supplies.
This block contains four independent choke input power supplies. In
each, the pulse output of the power transformer 1s rectified and ap-
plied to a filter choke and then to a filter capacitor. The output
voltages are as shown on the block diagram in figure
1.
Note that only
the +5 volt supply is sensed and regulated by the Power Supply Control
PCA. The other voltages track the sensed supply and are kept within
their accuracy tolerances without actually being sensed and regulated
independently.
3.2 POWER
SUPPLY
CONTROL peA.
3.2.1
3.2.2
3.2.3
The Power Supply Control PCA contains the low-level logic of the power
supply. It generates the
~ystem
Clock (SYS CLK) signal, senses and
regulates the +5 volt power supply output, limits the power supply pri-
m~ry
current, and shuts down the supply if the power line VOltage drops
below the minimum line voltage specification (88.5
V).
Low Line Detector.
The low line detector senses the power line VOltage by sensing the
+16
volt supply which is proportional to the line voltage. If this voltage
drops below +11 volts (line voltage of 88 volts) the low line detector
shuts off the circuit that drives the chopper on the Power Supply PCA
and therefore shuts down the power supply.
Current Limit.
The current li~it block senses primary current of the main power trans-
former and shuts off the chopper if the current becomes excessive.
Both the current limit and low line detector use a timer in this bloCK
which attempts to restart the power supply once per second so that the
power supply will restart itself if the fault condition is corrected.
Base Drive Steering.
This block takes the output pulses from the Voltage variable one-shot
and causes them to alternate between the two drive lines Which go to
the chopper. These signals cause the chopper transistors to be alter-
nately turned on. The base drive steering circuit is also designed to