Switched Mode Power Supply Measurements

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Osborne Knight
6 years ago
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1 Power Analysis 1

2 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

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

4 Line Voltage Line Current Line Power 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

6 Power supply efficiency measurement

7 Safe Operating Area Mask Testing

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

9 Energy Loss Loss displayed in Joules

10 Power Loss Loss displayed in Watts Power = Energy / Time

11 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

12 Solution 1: Overdriving the Signal 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 Differential Amplifier Differential Probe

13 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

16 Using High Definition Oscilloscopes 12-Bit Capture 8-Bit Capture

17 Using High Definition Scope with High Accuracy Probes 12-Bit Capture, 1% accuracy Probe 12-Bit Capture, Standard Probe

probes with high accuracy and high CMRR.

18 Example Hardware Configuration 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. CP030A and CP031A HVD3102 and HVD3106

19 Rds On Resistance Measurement Overdrive recovery of differential amplifier and high resolution oscilloscope combination

20 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

21 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

remove propagation delay differences between voltage and

22 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

measurement error Device turn-off transition loss, V x I, is

23 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 nj without proper deskew

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

25 Power Analyzer BH Curve

26 Power Analyzer BH Curve

28 BH Curve Definition

Voltage Current B= V(t)dt H = ni l B-H Curve shows the hysteresis loop for the magnetic material in inductors and transformers Coil Characteristics Input: # of windings Cross sectional area Magnetic

29 Voltage Current B= V(t)dt H = ni l 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

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

Cycle 1 Period Cycle 2 Period Cycle 3 Period Cycle 4 Period Cycle 5 Period Cycle 6 Period Cycle 7 Period Cycle 8 Period Cycle 9 Period Voltage 2.001 ns 2.004 ns 1.991 ns 2.001 ns 1.999 ns 1.

32 Cycle 1 Period Cycle 2 Period Cycle 3 Period Cycle 4 Period Cycle 5 Period Cycle 6 Period Cycle 7 Period Cycle 8 Period Cycle 9 Period Voltage ns ns ns ns ns ns ns ns ns Time Period ns ns ns ns ns ns ns ns ns Time Parameter Track can be used to determine power supply modulation

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

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

37 Power supply ripple measurement

38 Radiated Immunity Testing

Radiated Immunity Testing - Real Time Functional Performance Evaluation Deviation detection of a device under test (DUT) during exposure to a disturbance Functional state of the DUT is output through

39 Radiated Immunity Testing - Real Time Functional Performance Evaluation Deviation detection of a device under test (DUT) during exposure to a disturbance Functional state of the DUT is output through non-conductive fiber optic cables Mechanical mode tuner Devices under test are exposed to electric fields high enough to effect operation of nonshielded equipment. Transmit and receive antennas generate a controlled electric field RF-hardened fiber optic transmitters

test criteria such as signal high level, signal low level, frequency, duty

40 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

41 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. Attenuating Tip Accessories Available in a variety of voltage ranges, e.g., +/-1V, +/-5V, +/-20V and +/-40V with a simplified pin socket termination Fiber Optic Cable A standard 1m length cable is provided, but longer ones may be purchased for use. De-modulating Receiver The optical signal is received and de-modulated to an electrical output to the oscilloscope with correct voltage scaling.

42 High Voltage Active Single-ended (Fiber Optic) Probes Parameter Bandwidth Voltage Range (SE) Voltage Range (CM) Loading Attenuation CMRR Value 60 MHz 2 to 80V Virtually Unlimited 1-10MΩ 34-22pF Z IN =50kΩ@100 khz 2x to 80x >140 db A new topology specifically for measuring small signals floating on a HV DC bus

43 Power Integrity Example Jitter on a 10 MHz clock circuit is traced back to a 2.9 MHz Point-of-load (POL) DC-DC converter

44 Overview of DUT Power Delivery System for a Wireless Router Point-of-Load (POL) DC-DC converter Power delivery network Switched-mode AC-DC power supply

45 2.9 MHz POL DC-DC Converter Spectral Measurements The oscilloscope Spectrum Analyzer capability is used to detect frequency peaks of the POL Short 20 GS/s Long Acquisition 250 MS/s Spectrum Analyzer Table Peak Markers Correspond to Table

of 10 MHz clock acquisition Histogram of TIE measurements TIE Jitter vs.

46 POL Ripple Contributes to Clock Jitter JitterKit can be used to quantify jitter on 10 MHz clock and trace it back to the POL 10 MHz clock acquisition (500 μs long) TIE Jitter Overlay of 10 MHz clock acquisition Histogram of TIE measurements TIE Jitter vs. time for the 10 MHz clock TIE Jitter Spectrum of 10 MHz Clock Spectrum Analysis Table from 2.9 MHz POL February 15,

47 Power Rail Probing

attach and leave in place for quick and easy connection to cable) MCX to SMA Adapter MCX to U.

48 RP4030 Active Voltage/Power Rail Probe ProBuscompatible amplifier SMA to MCX short cable MCX Solder-in Lead (4 GHz) (can be soldered-in and left in circuit) MCX PCB Mounts (4 GHz) (good for larger circuit boards attach and leave in place for quick and easy connection to cable) MCX to SMA Adapter MCX to U.FL Lead (3 GHz) (attaches to compact U.FL PCB Mounts). U.FL PCB Mounts (compact size for dense, mobile or handheld systems)

49 Acquiring DC Power/Voltage Rails 5 mv/div 1.8 V offset 5 mv/div 1.8 V offset 1.8 V 0 V Coaxial Cable Input Terminated at 1 MΩ 1.8 V 0 V Passive Probe February 1, Power Rail Probe 1.8 V 0 V 5 mv/div 1.8 V offset Active Voltage Rail Probe

50 Motor Drive Analysis

51 Motor Drive Analysis Test Configuration Examples AC Induction Motor 2-wattmeter test configuration Brushless DC Motor test configuration

measurement analysis) Select the analog channel to use for Torque sensing input Speed & Angle setup changes depending on Method selected Angle is

52 Mechanical Setup Torque Sensing Method Selection Select Units, Filter Cutoff, and Scaling Speed, Angle, Direction Method Selection 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 input Speed & Angle setup changes depending on Method selected Angle is the arbitrary shaft rotation angle. Offset Angle allows correction to something not arbitrary (e.g. rotor field) Enable Zoom+Gate button and indicator (gray when ON )

53 Dynamic Motor Analysis

Record Length Acquisitions All table data is calculated on zoomed area only Displayed Sync

54 Dynamic Power Analysis - Zoom+Gate Operation Push Zoom+Gate button to create Zooms and Gate the Numerics table to zoomed area Zoomed Area in Acquisition Zooms Original, Full Record Length Acquisitions All table data is calculated on zoomed area only Displayed Sync Signal is Zoomed Per-cycle synthesized Waveforms are Zoomed Light Glows ON when in Zoom+Gate mode

55 Dynamic Drive Response Analysis

56 Efficiency Measurement on AC-AC 480V Motor Drive

Application example: Battery-powered brushless DC drill Waveforms captured from a battery-powered brushless DC drill. The Q-Scape tabs are labeled DC Bus, Drive Output, Mechanical, and Torque & Speed.

57 Application example: Battery-powered brushless DC drill 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.

Robotics Application Using Resolver for Speed and Angle Sine and cosine signals from the resolver Plot of Speed and Angle calculated per-cycle by MDA 8 khz excitation frequency for the resolver.

58 Robotics Application Using Resolver for Speed and Angle Sine and cosine signals from the resolver Plot of Speed and Angle calculated per-cycle by MDA 8 khz excitation frequency for the resolver. The Sync signal for the speed and angle measurements is this 8 khz excitation frequency. 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.

59 Motor test area (exterior view)

60 Motor test area (exterior / interior view)

61 Motor test area (interior view)

62 Motor test area (interior view)

63 Motor test area (interior view)

64 Motor drive analyzer testing 3 voltage phases and 3 current phases

65 Control room for motor test

Measurement and Analysis for Switchmode Power Design

Measurement and Analysis for Switchmode Power Design Switched Mode Power Supply Measurements AC Input Power measurements Safe operating area Harmonics and compliance Efficiency Switching Transistor Losses