HP 9020 User Manual

2-6 Theory of Operation
Ac Module
The ac module has an attached 6-foot line cord that plugs into an ac outlet. The line filter reduces
conducted emissions from the power supply assembly.
It also presents the ac voltage to the on/off
power switch/circuit breaker which enables/disables ac power to the computer.
The trip point of the circuit breaker depends
on which power configuration is being used. The 110V
breaker trips at 15 amps line or line overvoltage. The 220V breaker trips at 10 amps. Reset the
circuit breaker by turning the switch off
and then turning it back on.
Primary Board
After being rectified, the ac to the primary board charges two 2800,..dd capacitors. Each capacitor is
charged to 150-200V, depending on the line voltage and load.
The rectified dc voltage from the capacitors feeds a switching regulator. The regulator drives current
through the main power transformer.
Rectifiers at the output of the main power transformer develop the
+ 5V switching supply. This
supply provides
+ 5V for use throughout the computer. The + 5V output is monitored by the
supervisor board for overvoltage
and undervoltage. Also, the + 5V output feeds the pulse width
modulator. The modulator output controls the base drive which
in turn controls the switching
transistors. The pulse-width-modulator-enable signal
(PWM ENABLE) from the supervisor board
enables the modulator as long as no fault signal
is present. A fault signal disables the modulator,
shutting down the power supply assembly.
The main power transformer has another secondary winding that provides raw power to the
secondary board. This power
is used to generate the unregulated + 19V and - 19V which in turn
generate
all the other secondary supplies.
The low line detector circuitry monitors the voltage
on the secondary winding of the main power
transformer. That voltage
is transferred to the supervisor board where it is compared to a reference
voltage. If the voltage
on the secondary winding drops too low, a power-fail-warning (NPFW) is
sent to the processor. This provides a 4 to 8 ms warning before the power is actually shut down by
the fault circuitry.
The
peak power monitor is a current sense transformer in series with the main power transformer
primary winding.
Its purpose is to protect the switching transistors from damage due to an excessive
power condition. When the current exceeds
9A, the monitor generates a fault signal to shut down
the power supply assembly.
A
+ 16V bias supply provides power to various monitor and control circuits throughout the power
supply assembly. This supply stays active when the power supply
is shut down due to a fault
condition.
it controls the power supply LEDs and governs power supply start -up.
Secondary Board
Power from the main power transformer on the primary board is transferred via bus bars to the
secondary board. There, a
tapped rectifier converts the raw ac power into unregulated + 19V and
- 19V dc. These voltages in turn operate several switching regulators and one linear regulator. The
voltages produced, which are used throughout the computer, are
+ 12V, - 12V, + 6V, + 3V, and

HP 9020 Specifications

General

Brand	HP
Model	9020
Category	Desktop
Language	English