Specifications

6
Use Down Programming to Increase Test
Speed
Under light or no load conditions, a
power supply’s output capacitor dis-
charges slowly. If you’re using the
supply as a static voltage source, this
is not problematic, but when you’re
making tests at varying voltage levels,
slow discharge means slow tests.
Down programming circuits in power
supplies rapidly decrease the output
voltage, reducing discharge times by
hundreds of milliseconds. Agilent
Technologies power supplies use two
types of down programming circuits:
• In Figure 1, an FET is placed
across the output terminals.
Whenever the output voltage is
higher than the programmed value,
the FET activates and discharges
the output capacitor. The FET can
sink currents ranging from 10% to
20% of the supply’s output current
rating. The maximum load at low
voltages is limited to the On resis-
tance of the FET plus the series
monitoring resistor, resulting in a
slight degradation of the down
programming current near zero
volts.
• In Figure 2, the down programmer
lies between the power supply’s
positive terminal and a negative
source. This configuration pulls
the output completely down with
no degradation near zero.
Some power supplies, such as the
Agilent 662xA and 663xB series, can
sink currents equal to their full out-
put current rating. In the 663xB
series, this sink current is program-
mable, so you can use the supply both
as a programmable source and load—
very useful in applications such as
charging and discharging batteries.
Figure 1: A down programming circuit
with an FET across the output terminals
Figure 2: A down programmer situated
between power supply’s positive output
and a negative source
Tip
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