Specifications

5
Use down programming
to increase test speed
Tip
4
Under light or no load conditions,
a power supply’s output capacitor
discharges 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 percent to
20 percent of the supply’s output
current rating. The maximum load
at low voltages is limited to the
On resistance 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 663xA series, can sink
currents equal to their full output
current rating. This sink current is
programmable, so you can use the
supply both as a programmable
source and load.
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