Datasheet

Application Note
www.tektronix.com/power2
Historically, characterizing the behavior of a power supply
meant taking static current and voltage measurements with a
digital multimeter and performing painstaking calculations on
a calculator or computer. Today, most engineers turn to the
oscilloscope as their preferred power measurement tool.
This application note will describe common switch-mode
power supply measurements, shown in Figure 1, using a
Tektronix MDO/MSO/DPO4000 or MDO/MSO/DPO3000
Series oscilloscope. With the optional power measurement and
analysis software, these oscilloscopes provide automated power
measurements for fast analysis and simplified setup and deskew
of probes for maximum accuracy.
Preparing for Power Supply
Measurements
Ideally, a power supply would operate exactly as designed
and modeled. In reality, components are imperfect; loads vary;
line power may be distorted; environmental changes alter
performance. Power supply design is further complicated by
demands to increase performance, improve efficiency, reduce
size and cut cost.
Given these design challenges, the measurement system must
be setup correctly to accurately capture waveforms for analysis
and troubleshooting. Important items to consider are:
Oscilloscope Acquisition Modes
Eliminating Skew Between Voltage and Current Probes
Eliminating Probe Offset
Current Probe Degauss
Bandwidth Limiting Filters
Figure 1. SMPS Components that are Characterized with Power Analysis Software.
Line
Voltage
Output
Voltage
Feedback
Input Filter
V
IN
V
OUT
Power Quality
Harmonics Analysis
Total Harmonic Distortion
Switching Loss
Safe Operating Area
di/dt, dv/dt
Ripple
Switching Device
Control Circuit
Modulation Anaylsis
PWM
Rectifier & Filter