HP 3000 SERIES II System Service Manual page 169

System Service
B-4. BLOCK DIAGRAM DESCRIPTION. Figure B-1 is a block diagram of the power supply. The
following paragraphs describe the operation of each of the blocks shown in the figure.
B-5 Primary Power Circuit. The AC line voltage enters the power supply through a connector
and passes through a 5-ampere fuse and radio frequency interference (RFI) filter to the POWER
switch. The POWER switch is located on the front panel of the power supply. With the POWER
switch in the ON position, line voltage is applied to the preregulator, cooling fan, and a step-down
transformer. The fan and transformer circuit are protected by a I-ampere fuse.
B-6. Preregulator A9. The preregulator contains a silicon controlled rectifier (SCR) bridge that
converts the AC line voltage to a unidirectional, pulsed voltage. The pulsating voltage is filtered to
become the regulated +130 volt rail voltage. The rail voltage is applied to the inverters and is used as
a basis for all DC output voltages. The SCR bridge is controlled by the preregulator control circuit
through an isolating transformer.
B-7. Preregulator Control AI. The stepped-down line voltage is applied to full-wave rectifiers
which supply unregulated +22, -22, and +9 volts DC for the bias voltage regulagors. The regulators
provide internal power supply bias voltages. The preregulator control circuit uses the AC line
frequency, -30 volt DC feedback, and status of the current limiter and voltage protect circuits. The
preregulator control circuit supplies trigger pulses to the preregulator that determine the "on" time
of the SCR bridge circuit to maintain proper control of the 130 volt DC rail.
B-8. Inverter A7. The inverter circuits convert the 130 volt DC output of the preregulator to a
square-wave AC voltage which is transformer-coupled to the rectifiers. The transformer coupling
provides isolation for stages following the inverter. The 800-Hertz operating frequency of the
inverter is determined by the inverter driver. There are two inverter circuits within the inverter that
operate 90 degrees out of phase with each other. Each circuit is fused for 3 amperes.
B-9. Inverter Driver A2. The inverter driver generates an 800-Hertz, two-phase clock which is
timed to develop phase 1 and phase 2 drive signals. The two inverter driver circuits are
transformer-coupled to the two inverter circuits.
B-I0. Full-Wave Rectifiers and Filters. The transformer-coupled inverter output is rectified and
filtered to provide DC outputs of +15, +5, -5, and -15 volts DC. Additionally, +30 and -30 volts
DC are supplied to the +20 and -20 volt regulators.
An
independent -30 volt output is fed back to the preregulator control circuit to maintain output
voltage regulation.
B-ll. 20-Volt Regulators. The 20-volt regulators consist of a +20 and a -20 volt regulator. The
+20 volt regulator is a switching regulator which converts the +30 volt rectifier output to a
regulated +20 volt DC output. The-20 volt regulator is a series regulator which converts the -30
volt rectifier output to a regulated -20 volt DC output. The +20 and -20 volts DC are used by a
power supply for the semi-conductor memory. An analog signal from the memory power supply is
used by the +20 volt regulator to control the output voltage. The -20 volt regulator is designed to
track the +20 volt regulator so that the two outputs are equal and opposite in polarity.
B-4
JAN 1977