EG&G ORTEC 4002A Instrukcja obsługi i serwisowania - Strona 8
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Drukuj stronę4. OPERATING INSTRUCTIONS
The available current from the power supply is specified in
Section 2, "DC OUTPUT." Care must be used to ensure
natural convection of heat dissipated by the heat sinks and
power transformer. When used at maximum power load
ings on a bench or table top, the bin and power supply
should be in an open space, placed upon blocks at least
1 in. off the table mounting surface to allow maximum
ventilation. When used in a rack, attention should be
paid to placement of other heat-generating equipment.
Adequate unobstructed space on all sides is necessary
for convection ventilation and cooling. If the bin contains
other heat-generating equipment, a blower may be ad
visable to remove the dissipated heat.
When it is necessary to rack mount several bins and power
supplies, especially when other heat-generating equip
ment is located within the rack, the term "ambient temper
ature" becomes less clearly defined. A better guide to
maximum power loading capability is to monitor the heat
sink temperature. Never allow the heat sink tempera
ture to continuously run above 85° C. Although this is not
the maximum operating temperature, any additional
temperature rise due to other conditions of the system
may force the supply out of tolerance and may cause it to
automatically shut down operation. Should your opera
tion produce a temperature of 85° C, a blower to remove
the heat is necessary. The EG&G ORTEG Model M127/N
Rack-Mountable Cooling Fan is recommended in this
situation.
5.
CIRCUIT DESCRIPTION
The 4002A power supply produces four dc output volt
ages. A power transformer changes the input ac line
voltage into four separate low-voltage sources.
The
sources or windings are full-wave-rectified, capacitor-
filtered, and regulated by electronic series regulator cir
cuits. The regulator circuits provide short circuit and cur
rent limiting protection.
Each of the four series regulator circuits are identical in
operation; they are physically different only in component
vaiues for each supply. The regulator can operate in
two modes: First and normal is the voltage regulation
mode; second is the current-foldback or current-limiting
protection mode.
The regulator will operate in the voltage regulation mode
at any current output up to and including the full rated
output of a particular supply. When current output beyond
—150% of the rated output is required, which includes a
direct short across the output terminals, the regulator
automatically converts to a current-foldback mode. This
provides power limiting and protection of the regulator's
circuitry and components.
When excessive current
demands are removed, the regulator resumes the voltage
regulation mode.
For a description of the regulator refer to the schematic
at the back of this manual. For convenience, only the
+24 V regulator will be discussed. An explanation of
the regulation in the normal voltage regulation mode
is given.
A 6.9 V reference voltage is set by the precision reference,
U1. This reference voltage is divided by R3and R4and fed
to pin 3 of the controller, U2. Simultaneously the output is
divided by R8, R9, and RIO, fed to pin 2 of U2, and com
pared with the voltage at pin 3 to produce an error signal
at pin 6. Pin 6 of U2 drives the darlington transistor,
Q1, to maintain the same voltage at pins 2 and 3. Line reg
ulation is improved by the zener regulator, 04, which
receives its unregulated voltage from a voltage-doubler
circuit consisting of 01, 02, 01, and 02.
Ourrent flow to the output is monitored by sensing the
voltage drop across R11. When the potential between pins
10 and 1 of U2 exceeds —80 mV, the output current and
voltage will decrease, limiting the power dissipated in 01.
Oapacitors 04, 16, and 5 tailor the frequency response of
the system to provide excellent recovery time and output
impedance characteristics. 05 provides reverse-current
protection for the power supply and load in the event that
a voltage source of the wrong polarity is connected to the
output terminal. If loss of the sense lead should occur
(pin 3 of 0N2 or pin 13 of PGM) R47 provides continued
operation with some loss of regulation.