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Chapter 7 Power and Signal Distribution
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
7-2
7.2.1 POWER SUPPLY ASSEMBLY
The 76-watt power supply assembly is contained in a single unit that features a selectable input
voltage of 90-132 VAC and 180-264 VAC. The power supply assembly provides +3.5 VDC, +5
VDC, -5 VDC, +12 VDC, and -12 VDC potentials for the system board, expansion board(s), and
installed drives. These voltages are controlled by the PS On signal from the Power Control Logic.
A fault-detection circuit automatically shuts down the power supply when certain faults are
detected. Faults that can trigger the protection circuitry include:
♦ Overvoltage - The +5 VDC output will activate the overvoltage crowbar circuit that triggers
the protection circuit when the output exceeds +5.60 VDC to +6.80 VDC. The +3.5 VDC
output will activate the overvoltage crowbar circuit when the output is sensed to be in the
+3.7 VDC to +5.0 VDC range.
♦ Short Circuit - The protection circuit triggers if any power supply output is shorted to
ground or to another output. This function reduces shock or fire hazard
In addition to the previously mentioned voltages, auxiliary +5 VDC (+5 AUX) is produced by the
power supply assembly as long as the unit is plugged into a live AC outlet. The +5 AUX voltage
is used by power control logic and the network interface controller.
Table 7-1 shows the specifications for the power supply.
Table 7–1. Power Supply Specifications
Table 7-1.
Power Supply Assembly Specifications
Parameter
Tolerance/
Range
Min. Current
Loading [1]
Max.
Current
Surge
Current [2]
Max.
Ripple
Input Line Voltage:
110 VAC Setting:
220 VAC Setting:
90 - 132 VAC
180-264 VAC
--
--
--
--
--
--
--
--
Line Frequency 47 - 63 Hz -- -- -- --
Steady State Input (VAC) Current: -- -- 5.5 A -- --
+3.5 VDC Output +/- 1% 0.6 A 7.0 A 7.0 A 50 mV
+5 VDC Output +/- 5 % 0.5 A 5.0 A 5.0 A 50 mV
+5 AUX Output +/- 5 % 0.1 A 1.2 A 1.2 A 80 mV
+12 VDC Output +/- 5 % 0.0 A 1.5 A 3.0 A 120 mV
-12 VDC Output +/- 10 % 0.0 A 0.2 A 0.2 A 200 mV
NOTES:
[1] Minimum loading requirements must be met at all times to ensure normal operation
and specification compliance.
[2] Surge duration no longer than 10 seconds and +12 tolerance +/- 10%.
The system fan is physically attached to and driven by the power supply. Fan speed is adjusted in
a linear fashion (5.5-13.6 VDC) by the power supply. The power control logic also controls fan
operation through an LM75 temperature sensor. This sensor controls the FAN OFF signal that
indicates to the power supply to shut off the fan. A temperature sensor within the power supply
can cause the power supply to override the FAN OFF signal if the ambient temperature of the
power supply is too warm.