HP 8153A - Secondary Regulation; Overvoltage Protection and Low Voltage Detection; Display Board

Secondary regulation The coarse regulation of the power supply is determined by the
voltage at UI02 pin 1. This voltage comes from TIOI pins 5 and 6, is
rectified by CRI06 and then fed, via voltage divider R1l8, R1l9 and
R120, to the sense input pin l of UI02.
As the +5 Volt DC is the most critical voltage, it is also sensed
directly at its output (schematic 3B). The +5 Volt, sensed via R153,
RVl56 and R155, is applied to the regulation amplifier input of
UI09. In UI09 it is compared to an internal voltage reference of
approximately 2.75V. The output current of UI09 then controls the
current through R1l8 via the opto coupler UI03 (schematic 3A). The
voltage across R1l8 is applied to the sense input at UI02 pin 1.
Overvoltage Protection and Low Voltage Detection
The primary side of the power supply is protected against overvoltage
by voltage suppressor diode VSIOO. This suppressor diode will
produce a constant short and blow the main fuse if the line voltage
increases above 275 Volt RMS.
To protect the circuits supplied by the power supply against
overvoltage, the DC supplies also use voltage suppression diodes
to avoid possible damage. VSI03, VS122, VSl23 and VSI02 with
different breakdown voltages short the corresponding DC voltages
in the case of too high a voltage being supplied from the switching
transformer TI01.
A line voltage decrease below the specified value is detected by UI02
pin 3. This is sensed via the voltage divider RIll,R1l2 and R1l4.
Display Board
This information deals with schematic 4.
The dìsplay board contains the 2 shift registers UIOI, UI02 and the
Vacuum Fluorescence Display (VFD, UI03). The serialized display
data DSHIFT from the KID UIOI (schematic lE) are shifted into the
high voltage grid drivers UIOI and UI02. The parallel output data
then control the grids and segments of the VFD.
Theory of Operation 1·5