HP 3000 III Series Manual page 338

HP 32421A Series
I I I
Power Supplies
9-4. 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.
9-5. Preregulator Control A1
The stepped-down line voltage is applied to full-wave rectifiers
which supply unregulated +22, -22, and +9 volts dc for the bias
voltage regulators. 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 lim-
iter and voltage protect circuits. The preregulator control cir-
cuit supplies trigger pulses to the preregulator that determine
the "on" time of the SCR bridge circuit to maintain proper con-
trol of the +130-volt dc rail.
9-6. Inverter A7
The inverter circuits convert the 130-volt dc output of the pre-
regulator to a square-wave ac voltage that is transformer-coupled
to the rectifiers. The transformer coupling provides isolation
for stages following the inverter; The aOO-Hz operating fre-
quencyof the inverter is determi.ned by the inverter driver.
There are two inverter circui ts wi thin the inverter that operate
90 degrees out of phase with each other. Each circuit is fused
for 3.0 amperes.
9-7. Inverter Driver A2
The inverter driver generates an aOO-Hz, two-phase clock which is
timed to develop Phase 1 and Phase 2 drive signals. The two in-
verter driver circuits are transformer-coupled to the two in-
verte r circu its.
9-8. 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. Addi-
tionally, +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
re gulation.
9-9. 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
9-4