Model DMM7510 7½ Digit Multimeter Application Manual
Section 7: Capturing and analyzing waveforms
DMM7510-904-01 Rev. D March 2021
7-3
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 power before connecting DUTs. 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 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 (safety ground) 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. Failure to follow these
guidelines can result in injury, death, or instrument damage. Failure to recognize and observe
normal safety precautions could result in personal injury or death.
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 uses the Texas Instruments LM25088MH-1/NOPB evaluation board to demonstrate
the digitizing capabilities of the DMM7510. Modifications were made to the evaluation board to
generate a 50 kHz switching frequency. An input voltage of 12 V is used on all subsequent tests.
Since the maximum output current of the evaluation board is 3 A, different resistive loads can be used
to achieve a variety of loading effects, as shown in the following tests.
