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Keysight Technologies
Methods for Characterizing and Tuning
DC Inrush Current
Application Brief
Introduction
Inrush current or input surge current refers to the momentarily large surge current that occurs when
you irst turn on power to a device. Inrush current often occurs in devices with a large amount of
parallel capacitance at the input, such as DC-to-DC converters or devices with extremely low imped-
ance under transient conditions, such as electric motors. Inrush current can be several times larger
than the device's steady-state current. For instance, electric motors can have inrush current levels
25 times greater than their steady-state current levels.
When you characterize inrush current, you either capture a high-resolution digitized proile of a
device's inrush current or just capture a reliable peak current reading. The traditional method for
characterizing inrush current combines a power supply, a digitizer or scope, and a current shunt or
current probe. In this measurement brief, we will look at using a modern performance power supply
for characterizing inrush current and compare it with the traditional method.
Snapshot
An automotive company is updating its test system for electronic control unit (ECU) testing. Its
engineering team scrutinizes the test plan to ind ways to increase throughput and reduce test system
complexity without reducing test integrity. The team identiies the inrush current measurement as a
candidate for improvement. The system currently employs a power supply, a current shunt and
digitizer, and switching to automate the inrush current measurement. The team decides to replace this
setup with the Keysight Technologies, Inc. N7951A dynamic DC power supply. The N7951A is a fast
power supply with a built-in high-resolution digitizer. N7951A provides them with a single-instrument
solution that speeds up test, reduces test system complexity, and delivers higher accuracy than their
old method for measuring inrush current.
03 | Keysight | Methods for Characterizing and Tuning DC Inrush Current - Application Brief
Methods for Characterizing Inrush Current switch open to allow the supply to ramp-up to the set
voltage level. Once that is accomplished, closing the
Main reasons why characterizing inrush current is necessary switch would apply the voltage to the DUT. Even with
in many test applications: the switch, problems can still surface. If the supply's
transient response is poor, its voltage level will droop
1. Device protection