Model DMM7510 7½ Digit Multimeter User's Manual
Section 10: Capturing and analyzing waveforms
DMM7510-900-01 Rev. B / May 2015
10-3
To prevent electric shock, test connections must be configured such that the user cannot
come in contact with test leads or any device under test (DUT) that is in contact with the
conductors. It is good practice to disconnect DUTs from the instrument before powering the
instrument. Safe installation requires proper shields, barriers, and grounding to prevent
contact with test leads.
There is no internal connection between protective earth (safety ground) and the LO
terminals of the Model DMM7510. Therefore, hazardous voltages (more than 30 V
rms
) can
appear on LO terminals. This can occur when the instrument is operating in any mode. To
prevent hazardous voltage from appearing on the LO terminals, connect the LO terminal to
protective earth if your application allows it. You can connect the LO terminal to the chassis
ground terminal on the front panel or the chassis ground screw terminal on the rear panel.
Note that the front-panel terminals are isolated from the rear-panel terminals. Therefore, if
you are using the front-panel terminals, ground to the front-panel LO terminal. If using the
rear-panel terminals, ground to the rear panel LO terminal.
Testing a buck converter
A buck converter is a highly efficient switch mode DC-to-DC voltage step-down converter. It stores
energy in the form of a magnetic field on an inductor. In the on state, the switch is closed and the
input voltage charges the inductor. In the off state, the switch is open and the inductor discharges the
stored energy as current flow through the load. Some of the key measurements involved in testing a
buck converter are:
•
Ripple noise on the output voltage
•
Duty cycle from switch node voltage
•
Inductor current linearity with varying load
•
Power-up behavior
The following test will use the Texas Instruments LM25088 evaluation board (EVM) to demonstrate
the digitizing capabilities of the Model DMM7510. Modifications were made to the LM25088
evaluation board to realize a 50 kHz switching frequency. An input voltage of 12 V is used on all
subsequent tests.
Since the maximum output current of the LM25088 is 3 A, different resistive loads can be used to
achieve a variety of loading effects, as shown in the following tests.
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