Product specifications

123
Power Products 10 Most frequently asked questions about using
Applications Information DC power products
(Continued)
More detailed specifications at www.agilent.com/find/power
quantities (volts and amps). This
resulting quantity will never be
smaller than the watts demanded
by an instrument. Uninformed users
incorrectly use VA to assess the
device’s over-all efficiency and power
demands. VA is most frequently and
correctly used by electricians to
determine proper AC mains conduc-
tor gage and circuit breaker sizing.
4
How much cooling do I need for my
power supply?
Users frequently rack power supplies
into an enclosure to supply power to
some remotely located external load.
Under these conditions, to properly
determine the cooling requirements,
the systems integrator needs ther-
mal data from the manufacturer for
the specific enclosure in question.
This data is generally in the form of
a curve which relates the rise of the
enclosure’s internal air temperature
to the amount of power (or BTU’s)
dissipated within the enclosure.
The difference between the maxi-
mum power demanded by the
external load, and the AC power
demanded by the power supply
to support the load’s needs, is the
power dumped into the internal air
of the enclosure. Using this num-
ber and data for the enclosure, the
internal rise can be determined. The
internal rise added to the external
ambient temperature will determine
the temperature of the environment
for the power supply. This must be
within the ratings of the product or
premature failure will occur.
A valuable conversion factor
between Watts and BTU’s is listed
below:
1 BTU/Hr = 0.293 Watt
The N57xxA family draws cooling
air from the outside of the rack.
Thus, the air temperature is equal
to that of the room's environment.
Heated, cooling air is then exhaust-
ed into the inside of the rack. As
a result, these instruments will not
properly cool if the inside of the
rack is “pressurized”. The static air
pressure within the rack must be
equal to or less than the air pres-
sure in the room’s ambient.
5
Can Agilent power supplies sink current?
Yes! Sinking, or downprogramming,
is the ability of a power supply to
pull current into the positive power
terminal. Sinking is necessary to
discharge the power supply’s own
output capacitor, or the capacitors
that are part of an external load.
Sinking is particularly important,
for example, in printed circuit
board test systems. The relays in
test board systems typically must
be switched only when the power
supplies have discharged to zero
volts, to avoid arcing and burn-out
of the relay contacts. Sinking allows
the power supply outputs to go to
zero quickly, thus providing faster
test times, an important factor for
reducing overall test cost.
The value of the sink current is fixed
and is not programmable, with the
exception of the 6630 series, where
sink current is set to the same value
that is programmed for source current.
In general, sinking is provided to
improve a power supply’s transition
time from a higher to a lower con-
stant voltage operating level, and
is not intended to be a steady-state
operating condition.
Other models not listed here do not
have high powered down program-
mers. Instead, they are capable
of discharging the power supply
output capacitors but not sinking
current from the device under test.
Series Current Sinking
Capability
6620 Multiple Output 110% of source
current rating
6630 100 Watt 110% of source
current rating
6030 Autorangers 50 W/actual output
voltage in volts or actual
voltage in volts/0.05 ohms,
whichever is less
6640 200 Watt 25% of source
current rating
6650 500 Watt 20% of source
current rating
6750/6760 Dynamically controlled
50/100 Watt to maximize output down-
programming speed. 7 W
continuous dissipation,
300 W peak.