Technical data

108
Applications Information 10 Most frequently asked questions about using
dc power products
(Continued)
Power Products Catalog 2002-2003 For more detailed specifications see the product manual at www.agilent.com/find/power
Agilent Technologies
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 exter-
nal 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 number 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 sup-
ply. 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
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.
Series Current Sinking
Capability
6620 Multiple Output 110% of source
current rating
6620 Precision Output 110% of source
current rating
Series Current Sinking
Capability
6630 100 Watt 110% of source
current rating
6030 Autorangers 50 W/actual output
voltage in volts or actual
output voltage volts/0.05
ohms, whichever is less
6640 200 Watt 25% of source
current rating
6650 500 Watt 20% of source
current rating
6670 2000 Watt 50 W/actual output
voltage in volts or actual
output voltage in volts/
0.05 ohms, whichever
is less
6680 5000 Watt 50 W/actual output
voltage in volts or actual
output voltage in
volts/0.05 ohms,
whichever is less
6690 6600 Watt 50 W/actual output
voltage in volts or actual
output voltage in
volts/0.05 ohms,
whichever is less
6
I want to put a microswitch on the
safety cover over my UUT so that lifting
the cover will program my ATE power
supplies to zero volts and protect the
operator from harm. Do Agilent power
supplies have this capability?
Yes, all of the GPIB programmable
supplies in the 6030, 6640, 6650,
6670 and 6680 series have this capa-
bility built-in at no extra cost. It’s
called “Remote Inhibit” (RI). RI is
available as an option at extra cost
on the 6620 and 6630 series. A con-
tact closure or TTL low signal pro-
grams the output of the supply to
zero volts. The power supply can also
be programmed to generate a service
request (SRQ) via the GPIB in the
event that RI is pulled low.