Power Analysis

1

Switched Mode Power Supply Measurements

AC Input

Power measurements

Safe operating area

Harmonics and compliance

Efficiency

Switching Transistor

Losses

Measurement challenges

Transformer

B-H curve

Dynamic Control Loop

Step load and start up behavior

Output Ripple

AC Input – Line Power and Harmonics

AC In + + DC Out

PWM Controller

Feedback

Line Voltage

Line Power

Line Current

RMS line voltage, RMS line current,

real power, apparent power, power

factor and crest factor

Line Harmonic Analysis

Line harmonics

can be measured

against

compliance

standards like EN

61000-3-2

Power supply efficiency measurement

Safe Operating Area Mask Testing

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

Energy Loss

Loss displayed in Joules

Power Loss

Loss displayed in Watts

Power = Energy / Time

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

Differential

ProbeDifferential

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

Using Differential Amplifier for Saturation Measurements

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

Using High Definition Oscilloscopes

12-Bit Capture 8-Bit Capture

Using High Definition Scope with High Accuracy Probes

12-Bit Capture, Standard Probe 12-Bit Capture, 1% accuracy Probe

Example Hardware Configuration

CP030A and CP031A HVD3102 and HVD3106

• Voltage and current probes to match the accuracy of HDO scopes

• High voltage differential probes with high accuracy and high CMRR.

• Current probes offer high accuracy and low noise.

Rds On Resistance Measurement

Overdrive recovery

of differential

amplifier and high

resolution

oscilloscope

combination

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

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

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 probesLine up the knee of the

curve to deskew for

power measurement

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

AC In + + DC Out

PWM Controller

Feedback

Switched-Mode Power Supply

The transformer provides isolation between the power supply

input and output

Power Analyzer BH Curve

Power Analyzer BH Curve

BH Curve Definition

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

𝐻 =𝑛𝐼

𝑙

Voltage

Current

B= 𝑉(𝑡)𝑑𝑡

Control Loop Measurements

AC In + + DC Out

PWM Controller

Isolated Feedback

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

Load

disconnected

Pulse width begins to decrease

Track function plots

changing pulse

width

Settling time

Control Loop Measurements

AC In + + DC Out

PWM Controller

Isolated Feedback

Power supply ripple measurement

Radiated Immunity Testing

Radiated Immunity Testing - Real Time Functional Performance EvaluationDeviation detection of a device under test (DUT) during exposure to a disturbance

Devices under test

are exposed to

electric fields high

enough to effect

operation of non-

shielded equipment.

Transmit and receive

antennas generate a

controlled electric field

Functional state of the

DUT is output through

non-conductive fiber

optic cablesMechanical mode

tuner

RF-hardened fiber optic transmitters

Outside the reverberant chamber, oscilloscope masks test for acceptance criteria

Optical receiver

and O/E converter

16 channels performing mask test criteria such as

signal high level, signal low level, frequency, duty

cycle, and other criteria fit within tolerance limits

described in the test plan

High Voltage Fiber Optically-isolated Probe?

Amplifier/Modulating Transmitter

A frequency modulating optical transmitter is

used for signal and data transmission across

a fiber optic cable.

De-modulating Receiver

The optical signal is received

and de-modulated to an electrical

output to the oscilloscope with

correct voltage scaling.

Fiber Optic Cable

A standard 1m length

cable is provided, but

longer ones may be

purchased for use.

Attenuating Tip Accessories

Available in a variety of voltage ranges,

e.g., +/-1V, +/-5V, +/-20V and +/-40V with

a simplified pin socket termination

High Voltage Active Single-ended (Fiber Optic) Probes

A new topology specifically for measuring small signals floating on a HV DC bus

Parameter Value

Bandwidth 60 MHz

Voltage Range (SE)

Voltage Range (CM)

2 to 80V

Virtually Unlimited

Loading 1-10MΩ || 34-22pFZIN=50kΩ@100 kHz

Attenuation 2x to 80x

CMRR >140 dB

Power Integrity ExampleJitter on a 10 MHz clock circuit is traced back to a 2.9

MHz Point-of-load (POL) DC-DC converter

Overview of DUTPower Delivery System for a Wireless Router

Switched-mode

AC-DC power

supply

Point-of-Load

(POL) DC-DC

converter

Power delivery

network

2.9 MHz POL DC-DC Converter Spectral MeasurementsThe oscilloscope Spectrum Analyzer capability is used to detect frequency peaks of the POL

Short Acquisition @ 20 GS/s

Long Acquisition

250 MS/s

Spectrum

Analyzer

Table

Peak Markers

Correspond to Table

POL Ripple Contributes to Clock Jitter JitterKit can be used to quantify jitter on 10 MHz clock and trace it back to the POL

February 15, 2017 46

10 MHz clock acquisition (500 μs long)

TIE Jitter vs. time for the 10 MHz clock

TIE Jitter Overlay of

10 MHz clock

acquisition

TIE Jitter Spectrum of 10

MHz Clock

Histogram of TIE

measurements

Spectrum

Analysis

Table from

2.9 MHz POL

Power Rail Probing

RP4030 Active Voltage/Power Rail Probe

ProBus-

compatible

amplifier MCX PCB Mounts (4 GHz)(good for larger circuit boards – attach and leave

in place for quick and easy connection to cable)

MCX Solder-in Lead (4 GHz)(can be soldered-in and left in circuit)

SMA to MCX

short cable

MCX to U.FL Lead (3 GHz)(attaches to compact U.FL PCB

Mounts).

MCX to SMA Adapter

U.FL PCB Mounts(compact size for dense, mobile or

handheld systems)

Acquiring DC Power/Voltage Rails

Coaxial Cable Input

Terminated at 1 MΩ

February 1, 2017 49

5 mV/div 1.8 V offset

1.8 V

0 V

5 mV/div 1.8 V offset

1.8 V

0 V

Passive Probe

5 mV/div 1.8 V offset

1.8 V

0 V

Active Voltage Rail Probe

Power

Rail

Probe

Motor Drive Analysis

Motor Drive Analysis Test Configuration Examples

AC Induction Motor 2-wattmeter test configuration Brushless DC Motor test configuration

Mechanical Setup

Torque

Sensing

Method

Selection

Speed & Angle setup

changes depending on

Method selected

Rotation

direction is

arbitrary – select

one of these to

get correct sign

of rotation

parameter

Waveform period

synchronization setup (for

per-cycle measurement

analysis)

Select the analog channel to

use for Torque sensing inputEnable Zoom+Gate –

button and indicator

(gray when “ON”)

Select Units,

Filter Cutoff,

and Scaling

Speed,

Angle,

Direction

Method

Selection

“Angle” is the arbitrary shaft

rotation angle. “Offset Angle”

allows correction to

something not arbitrary (e.g.

rotor field)

Dynamic Motor Analysis

Dynamic Power Analysis - Zoom+Gate OperationPush Zoom+Gate button to create Zooms and Gate the Numerics table to zoomed area

Original, Full

Record

Length

Acquisitions

Zooms

Displayed

Sync Signal

is Zoomed

Per-cycle

“synthesized”

Waveforms

are ZoomedAll table

data is

calculated

on zoomed

area only

Zoomed Area

in Acquisition

Light Glows “ON” when in Zoom+Gate mode

Dynamic Drive Response Analysis

Efficiency Measurement on AC-AC 480V Motor Drive

Waveforms captured from a battery-powered

brushless DC drill. The Q-Scape tabs are labeled

DC Bus, Drive Output, Mechanical, and Torque &

Speed. 25 Mpt acquisitions are displayed on the left

and zooms displayed on the right.

The DC Bus signals are C3 (voltage) and C6

(current). The Drive Output signals are C1 and C2

(voltage) and C4 and C5 (current). The 2-wattmeter

method is used to calculate three-phase Drive

Output power. 12 bits and vertical zoom are used to

show the DC bus and current signals.

Torque is measured with C7 (from a dynamometer

torque load cell) and Speed is measured with C8

(analog tachometer from a dynamometer). Hall

sensors (Digital1) are also captured and could

measure speed.

Per-cycle synthesized waveforms showing

Mechanical Power, Torque and Speed are plotted for

the motor shaft output, and two XY plots are shown.

The XY plots show Torque vs. Speed (top) of the full

acquisition in pink (XY1: C7 vs. C8) and the zoomed

area (XY2: Z7 vs. Z8) in light green. XY3 shows Z7

vs. Z8 but in a different scale. It is common to want

to view Torque vs. Speed for a motor shaft output .

Application example: Battery-powered brushless DC drill

Robotics Application Using Resolver for Speed and Angle

300-pt Boxcar filter (300 points, ten 8 kHz periods with 30 points/period). 0 RPM is

the vertical grid center. As RPM goes positive, the motor shaft turns in one direction

(Angle or F6 slope is positive), and as RPM goes negative, the motor shaft turns in

the other direction (slope is negative). The Angle calculation resets to 0 degrees

whenever a full shaft rotation occurs.

Sine and cosine signals from the resolver

8 kHz excitation frequency for the resolver. The Sync signal for the speed and

angle measurements is this 8 kHz excitation frequency.

Plot of Speed and Angle calculated per-cycle by MDA

Motor test area (exterior view)

Motor test area (exterior / interior view)

Motor test area (interior view)

Motor test area (interior view)

Motor test area (interior view)

Motor drive analyzer testing 3 voltage phases and 3 current phases

Control room for motor test