Application Examples
106 TDS5000B Series Quick Start User Manual
Measuring Switching Loss in a Switch Mode Power Supply
(SMPS)
WARNING. To a void injury or death, use extreme caution when working with high voltage circuits. Only qualified
personnel should take measurements using high voltage circuits.
The switching loss in a power supply determines its efficiency. Using an oscilloscope to measure switching loss
is probably the mos t important and one of the most common ta sks a switch mode power supply des igner must
perform. To us e your TDS5000B Series oscilloscope to measure switching loss, perform the following steps:
1. Connect a P5205 (or other high
voltage differential probe) to
channel 1.
2. Connect a TCP202 (or other cur-
rent probe) to c hannel 2.
3. Connect the positive input of the
P5205 to the source voltage and
the negative input to the drain
voltage on the switching device to
measure V
ds
.
4. Connect the TCP202 to the drain
current to measure I
ds
.
Switching device
Drain
current
Drain
voltage
Source
voltage
1
2
3
4
5. Turn on CH 1 and CH 2.
The P5205 and TCP202 are a matched
set of probe s in terms of cable length,
so you should not nee d to deskew the
input channels. If you are using other
probes that are not mat ched, do the
following to perform a deskew
operation:
6. Select Deskew..., and then press
F1 for instructions on performing
a deskew operation.
5
6
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