This webinar covers the measurements of interest for designers of switched-mode power conversion circuits and devices. With the goal of high efficient and reliable designs, we review the acquisition of voltage and current, their relationship in switched-mode power conversion circuits. We review specific power circuit performance areas including the analysis of power device switching losses, conduction losses, dynamic on-resistance, control loop response, power quality, conducted emissions, best practices for probing power circuits, and power rail integrity measurements.

1. Power Measurement and Analysis
of Switched-Mode Power Supplies
Stephen Murphy
Senior Applications Engineer

2. Agenda
 AC Input
 Power quality measurements
 Harmonics and compliance
 Efficiency
 Switching Transistor
 Losses
 Safe operating area
 Measurement challenges
 Transformer
 B-H curve
 Dynamic Control Loop
 Step load and start up behavior
 Output
 Ripple
 Power Rail Integrity
 Best Probing Practices

3. AC Input – Line Power and Harmonics
AC In + + DC Out
PWM
Controller
Feedback

4. Line Voltage
Line Power
Line Current
RMS line voltage, RMS line current,
real power, apparent power, power
factor and crest factor

5. Line Harmonic Analysis
Line harmonics
can be measured
against
compliance
standards like
EN 61000-3-2

7. Three-Phase Power Analysis
 MDA800 Series Motor Drive Analyzer displays the mean power
values of the acquisition, or gated dynamic power measurements

8. 3-Phase Power Measurements - “Static” and “Dynamic”
 User-Configurable “Numerics” Results Table
 Selection of Rows and Columns Populates the Results Table
 Probe Line-Line (L-L) and Display Results in Line-Neutral (L-N)
 Using L-L to L-N conversion

9. Power supply efficiency measurement

10. AC In + + DC Out
PWM
Controller
Feedback
Switched-Mode Power Supply
DC AC
The measurements we will talk about here are useful for any
inverter based power conversion device

11. Power Conversion – Switching Device Characterization
Power conversion involves use of fast power electronics
semiconductor devices to convert power efficiently. These
devices are utilized in many different products and industries.

12. Switched-Mode Power Measurements – Single-Phase

13. Energy Loss
Loss displayed in Joules

14. Power Loss
Loss displayed in Watts
Power = Energy / Time

15. Conduction Loss Measurement Challenge
Although the peak to
peak waveform may be
hundreds of volts, during
the conduction stage the
voltage is close to zero.
Measuring the conduction
loss or dynamic on
resistance is a challenge
due to the limited
dynamic range of the
oscilloscope

16. Differential
Probe
Differential
Amplifier
Differential probe
response is very slow
to stabilize, and never
reaches the correct
saturation voltage level
Differential amplifier
response rapidly
stabilizes and reaches
the correct saturation
voltage level
Solution 1: Overdriving the Signal

17. Teledyne LeCroy DA1855A Differential Amplifier
 CMRR 100,000:1
 Overdrive recovery – 400 V
to 100 mV <100 ns
Precision Offset Generator
0.5%
DA1855A
Differential
Amplifier
Differential
Amplifier connected
to oscilloscope

18. Solution 2: Use High Definition Oscilloscope
 12-Bit Capture  8-Bit Capture

19. Solultion 3: Use HDO with High Accuracy Probes
 12-Bit Capture, Standard Probe 12-Bit Capture, 1% accuracy Probe

20. High Accuracy Differential Voltage and Current Probes
CP030A and CP031A HVD3102 and HVD3106
• New voltage and current probes to match the accuracy of HDO scopes
• New high voltage differential probes offer high accuracy and high CMRR.
• New current probes offer high accuracy and low noise.

21. Rds On Resistance Measurement
Excellent
overdrive recovery
of DA1855A
combined with
high resolution of
HDO provides
most accurate
measurement

22. Eliminating Sources of Error – DC Offsets, Deskew
 Before making detailed device loss measurements, fine adjust to
eliminate DC offset errors and scope probe propagation delay
differences

23. Two Ways to Fine Adjust Current Probe DC Offset
 During Off-state,
utilize Math
integral function
and adjust for
zero slope
 Utilize Power
Analyzer’s
automatic
calculation of
Off-State
Losses and fine
adjust to zero

24. Deskewing Voltage and Current Probes
Use a deskew calibration
source, with V and I
coincident edges, to
remove propagation delay
differences between
voltage and current
probes Line up the knee of the
curve to deskew for
power measurement

25. Sources of Error – Skew Between Voltage and Current Probes
 Timing skew between
voltage and current
probes results in
measurement error
 Device turn-off
transition loss, V x I, is
properly measured at
7.88 nJ of energy
versus 13.43 nJ
without proper deskew

26. Safe Operating Area Mask Testing

27. High-Side Gate Capture
 Probe Requirements:
 Isolation from power rail
 Low tip capacitance
 High input impedance
 High CMRR
 Low lead inductance
 Low attenuation

28. AC In + + DC Out
PWM
Controller
Feedback
Switched-Mode Power Supply
The transformer provides isolation between the power supply
input and output

29. B-H Curve shows the hysteresis loop for
the magnetic material in inductors and
transformers
Coil Characteristics Input:
• # of windings
• Cross sectional area
• Magnetic path length
Cursor are used to measure magnetic field
strength, H, and magnetic flux density, B
• H is calculated from the current, # windings
and magnetic path length
• B is calculated as the integral of the
voltage across the coil
Parameter math is utilized for calculation of
the magnetic permeability of the material
• B and H constants are individually entered
and the resulting parameter is calculated
as B/H
𝐻𝐻 =
𝑛𝑛𝑛𝑛
𝑙𝑙
Voltage
Current
B= ∫ 𝑉𝑉(𝑡𝑡)𝑑𝑑𝑑𝑑

30. Control Loop Measurements
AC In + + DC Out
PWM
Controller
Isolated
Feedback

32. 2.001 ns
2.001 ns
Cycle 1
Period
2.004 ns
2.004 ns
Cycle 2
Period
1.991 ns
1.991 ns
Cycle 3
Period
2.001 ns
2.001 ns
Cycle 4
Period
1.999 ns
1.999 ns
Cycle 5
Period
1.995 ns
1.995 ns
Cycle 6
Period
2.008 ns
2.008 ns
Cycle 7
Period
1.986 ns
1.986 ns
Cycle 8
Period
2.001 ns
2.001 ns
Cycle 9
Period
Time
Period
Time
Voltage
Parameter Track can be used to determine power supply modulation

33. Load
disconnected
Pulse width begins to decrease
Track function
plots changing
pulse width
Settling time

36. Output Ripple Measurements
AC In + + DC Out
PWM
Controller
Isolated
Feedback

37. Power supply ripple measurement

38. Measurement Example – 2.9 MHz POL Switching Regulator

39. Ripple Contributes to Jitter on Clock

40. Power Delivery System for a Wireless Router
Switched-mode
AC-DC power
supply
DC-DC
converter
Power delivery
network
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41. Acquiring DC Power/Voltage Rails
What is Required?
 High Offset
 HDOs have high levels of offset built-into the
oscilloscope
 +/-1.6V (1mV to 4.95mV/div)
 DC Coupling
 AC Coupling not available on high BW 50 Ω
scope inputs
 AC Coupling reduces lower frequencies of
interest
 1:1 Attenuation
 Probes with attenuation help with wider
offset range but increased scope
amplification can cause increased noise and
lower fidelity
 Workarounds like using oscilloscope offset
with a 50Ω 1x coaxial connection and
DC1MΩ scope termination results in limited
bandwidth, reflections due to impedance
mismatch, and potential impedance circuit
loading
1.8Vdc signal at 1
V/div with 0V offset
1.8Vdc signal at 5mV/div
with 1.8V offset
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42. PMIC Transient Rail Response Testing
Acquiring and Viewing the Transient Response
 Load is increased from ~0 to 20
Amps and the corresponding
DC Rail voltage is monitored to
ensure it is stable
 Usually a narrow tolerance
band, e.g. +/-20mVp-p on a
1.0Vdc bus.
 Overshoot, droop, noise, etc.
are also important to
understand
7 mV/div gain
setting with 1Vdc
offset
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DC Rail
Curren
t
20A
No-load (near 0A)
DC Rail
Voltage
Mean DC =
999.67mV
Mean DC = 1003mV

43. PMIC Transient Rail Response Testing, cont’d
Measuring the Transient Response
 Measurement Parameters with Gates
can be used to measure VdcRAIL
before and after load.
 999.67 mV before
 1003.00 mV after
 Measure Parameter can be used to
measure step load change
 20.436 A
 Zooms and measurement parameters
can be used to understand high-
frequency behaviors
 Z1 = VMIN at step (967.70 mV)
 Z5 = VMAX before step (1012.21 mV)
 Z7 = VMAX after step (1016.38 mV)
 Measure “Detailed Help Markers”
explain measurements
11/1/2016 43
DC Rail
Curren
t
DC Rail
Voltage
Mean DC = 999.67mV
Mean DC = 1003mV
12-bit
Resolutio
n

44. PMIC Transient Rail Response Testing
Understanding the Transient Response of a Load Release
 Monitored input signals included
 Simple DC Rails
 4 total (700mV, 900mV, 1.2V,
1.5V)
 Multi-phase DC Rail (1.0V)
 12V supply Rail
 Load Current (20A to 0A)
 PWM Clock
 8 Channels at 12-bits and 1 GHz
(HDO8108) is used
 Validating or finding issues can
be reached through this view
11/1/2016 44
PWM Clock
Frequency
900mV rail
700mV rail
1.5V rail
1.2V rail
1.0V multi-phase rail
12V input supply
Load current

45. Important Voltage Probe Specifications
 Bandwidth
 Voltage Dynamic Range
 Single-ended and differential
 Common-mode voltage, differential-mode voltage
 Voltage Offset Capability
 HV Isolation
 Probe Loading (Resistive, Capacitive, Inductive)
 Attenuation
 Common Mode Rejection Ratio (CMRR)

46. Types of Voltage Probes Commonly Used in Power Electronics
 Low Voltage
1. Passive, Single-ended
2. Active, Single-ended “FET”
3. Active, Single-ended “Rail”
4. Active Differential
 High Voltage
5. Passive, Single-ended
6. Active, Single-ended (fiber-
optic isolated)
7. Active, Differential
8. Active, Differential Amplifier
with matched probe pair
1 2 4
5 6
7 8
3

47. Available from Teledyne LeCroy - Power Software Options
 Single-Phase Power Analysis - Tools for easy oscilloscope
setups:
 Device Analysis – Switching and Conduction Losses, B-H, Rds(on)
and dv/dt
 Control Loop Analysis
 Line Power Analysis – power quality, line harmonics (EN 6100-3-2)
 Power Supply Performance
 Reducing Probe Errors
 Three-Phase Power Analysis
 Motor Drive
 Integrated motor mechanical
 speed, torque, position, control
 Power Quality and harmonics
 Power Management and Power Sequencing
 Power Rail Integrity
11/30/2016Company Confidential 47

48. Teledyne LeCroy HDO8000 Series Oscilloscope
The platform upon which our Motor Drive Analyzer is based
 8 analog input channels
 16 digital logic inputs optional
 12-bit HD4096 High Definition
Technology
 “16x closer to perfect”
 Up to 1 GHz
 At up to 2.5 GS/s on all channels
 Up to 250 Mpts/Ch acquisition
memory
 25 seconds of capture at 10 MS/s
HD4096 12-bit technology is being
deployed into 8 channels to meet the
needs of fast growing applications

49. HDO8000 General-purpose Embedded Test Capability
 Mixed-signal (MSO) option
 16ch, 250 MHz clock rate
 Serial Trigger/Decode
 19 different low-speed serial
trigger/decode solutions available
 Probing
 ProBus compatible – supports
over 30 different Teledyne LeCroy
probes
 Active/passive
 High voltage differential
(1000Vrms)
 Current
 Differential amplifiers
 Connect up to 8 current probes at
one time

50. Teledyne LeCroy Has Your Complete Solution
High Definition Oscilloscopes
 HDO8108
 8ch, 12-bit, 1 GHz
 MSO option
 Up to 250 Mpts/Ch
 Power Management, Power
Sequencing, Power Integrity
 HDO9404
 4ch, 10-bit, 4 GHz
 40 GS/s
 MSO model
 Power Integrity
11/1/2016 50

51. Any Questions?
Thank You for Your Attention!