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1、CHow to Get Clean DC Power Find and eliminate noiseeBookINTRODUCTIONHow to Get Clean DC PowerFind and eliminate noiseClean DC power is the backbone of stable systems.Without clean power,your device will experience instability and a shortened lifespan.But,clean power is hard to get.When designing you
2、r devices,you have to take power into consideration from day one.The power-consuming part of your device should have a specified tolerance for ripple and noise,and the power-supplying part of your device must be designed to meet that spec.Both the power-producing and power-consuming parts of your de
3、vice must function properly or your devices performance and stability will suffer.If youre a 1-person operation,you have total control over every aspect of your device.But,more than likely,clean power is up to a team of engineers working in tandem.Even if you are not responsible for every stage of y
4、our devices power production and consumption,by understanding the process from start to finish,you can help to ensure the success of your designs and more efficiently test your device.Both the power-producing and power-consuming parts of your device must function properly or your devices performance
5、 and stability will suffer.How to Get Clean DC Power|2AC-DC Power ConversionDC-DC Power ConversionTesting Your Device ConclusionContents There are three main stages of getting clean DC power.How to Get Clean DC Power|3Stage 1:AC-DCPower Conversion Nearly every device in existence will pull power fro
6、m the grid at some pointwhether its battery-powered or wallpowered.Explore chapter 1 to learn how to test the effectiveness and efficiency of your AC to DCconverters.STAGE 1GO TO STAGE 1 Stage 2:DC-DCPower Conversion The goal of a DC-DC converter is to turn an unregulated DC voltage into a regulated
7、 DC voltage.A regulated DC supply provides a constant voltage regardless of its load.Without regulated power,your device will lose performance or fail altogether.Read chapter 2 for the tests to help ensure your DC-DC designs meet design parameters.STAGE 2GO TO STAGE 2 Stage 3:Testing andProtecting Y
8、our PowerConsuming Device Theres no such thing as perfectly clean power.So,you have to test your device to see how well it handles a non-ideal power supply.Skip to this chapter to learn how to avoid damaging your device and tips for testing your devices noise tolerance.STAGE 3GO TO STAGE 3 Conclusio
9、n:AchievingClean Power Understanding the tests and tips covered in these three stages will help you eliminate more noise from your system.Now that you know how to get clean power,you can focus on your designs.CONCLUSIONGO TO CONCLUSION AC to DC Power ConversionSTAGE 1How to Get Clean DC Power|4DC-DC
10、 Power ConversionTesting Your Device ConclusionAC-DC Power ConversionSTAGE 1AC to DC Power ConversionAC to DC conversion is the first step in powering your devices.To get DC power for your wall-powered devices,you need to design or buy an AC to DC converter.Without a clean DC signal,your device can
11、be damaged or perform poorly.To make sure your power supply is supplying clean DC power,you need to verify a few crucial power supply attributes.Your testing should include:Input Power Analysis Switching Loss Analysis Output Power Analysis Efficiency Analysis Frequency Response AnalysisYou can use a
12、n oscilloscope to find defects and anomalies manually,but this wastes time that could be better spent on other parts of the design and verification process.Instead,many modern tools have built-in power supply measurements that will help you debug and verify your power designs more quickly.However,be
13、fore you can start evaluating your power supply,you need to make sure you are properly connected to your device.So,lets first explore best-practice probing techniques.If this has affected the first and last column spacing,select all of the first column,select the left border icon,and remove the bord
14、er.Select all of the last column,select the right border icon,and remove the border.Most engineers perform these measurements manually,but this wastes time that could be spent on other parts of the design and verification process.How to Get Clean DC Power|5DC-DC Power ConversionTesting Your Device C
15、onclusionAC-DC Power ConversionPower supply probing techniquesTo measure power with an oscilloscope,you need to measure both current and voltage(P=V x I).So,you need a current probe and a voltage probe that can safely measure your input voltageusually a high-voltage differential probe.The most commo
16、n type of current probe used for measuring power supplies is a clamp-on currentprobe.To make probing easier,you should either design-in a probe point for your current probe or solder a wire onto your device to create a temporary current loop for easy probe access(Figure 1.2).Once you have both curre
17、nt and voltage,use a math channel to calculate power(Figure 1.1).Figure 1.1.Math waveform(purple)shows power by multiplying the voltage(yellow)and current(green).When using current probes for a while,a magnetic field can build up and cause offset errors.To avoid this,demagnify(degauss)the probe and
18、zero the offset using the channel and probe menus on the oscilloscope.Some probes even have a button on the probe itself.Figure 1.2.A temporary current loop for easy probing.How to Get Clean DC Power|6Want to Learn More?Learn more about these probing techniques,and the recommended probes to use,see
19、the first section of the Switch Mode Power Supply application note.DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionInput power analysisIf your AC input is low quality or out of compliance,it can disrupt other connected devices.To characterize the input power quality,you sho
20、uld measure parameters such as real power,apparent power,and phase angle.You can perform these measurements using an oscilloscopes built-in power application.This will help you see if any distortion caused by the non-linear AC load will cause problems.Look out for sags or“dips”and swells on the volt
21、age waveform,since these can cause spikes of current that could be harmful to your device.Figure 1.3.Relationship between real,apparent,and reactive power.Reactive powerQ(VAR)Apparent powerS(VA)Real powerP(W)In addition to the above measurements,analysis of current harmonics is vital for device perf
22、ormance.If this specification does not fall within certain tolerances,the input power could cause other components connected to the AC supply grid to malfunction.To analyze harmonics,you need to visualize the amplitude of the frequency components that are going back into the AC grid.The best way to
23、do this is to set up an FFT measurement on the current waveform.The oscilloscopes FFT,or fast Fourier transform,enables you to view the frequency domain and the time domain at the same time,so its easy to analyze the amplitude of the frequency components.The current harmonics measurement built in to
24、 the power application on Keysight InfiniiVision oscilloscopes allows you to select an IEC standard for the harmonics specification.Then it compares the results against that standard and provides a colorcoded pass/fail indicator up to the 40th harmonic.Figure 1.4.FFT analysis of current harmonics us
25、ing the DSOX4PWR application.How to Get Clean DC Power|7Want to Learn More?Check out FFT and Pulsed RF Measurements to learn about FFTs and how to use this capability on an oscilloscope to analyze your signal.DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionSwitching loss an
26、alysisOnce you verify that the input power meets your specs,the next step is to examine the switching component of your supply.A power supply with an ideal switch will have no switching loss.However,the transistors used in power supplies are not ideal,so there will be some power loss as the switch o
27、pens and closes.Being able to analyze how much power is lost during the switch-on or switch-off will help you adjust your design to minimize that loss.To measure switching loss,use a differential probe to measure the voltage between the transistors drain and source(VDS)and a current probe to measure
28、 the current leaving the transistors source.The power loss signal is displayed on screen using a multiplication math function between the voltage and current channels.Math functions allow you to manipulate the waveforms to visualize something you wouldnt normally be able to see on an oscilloscope,li
29、ke power loss.Because power is a calculated value,the offset error is one of the biggest sources causing inaccuracy in power loss measurements.An offset error 0.1 division may seem small,but it can make a huge difference when trying to measure the loss during the conduction phase.If youre using a Ke
30、ysight InfiniiVision oscilloscope,use the builtin precision calibration procedure designed for switching lossmeasurements.Figure 1.5.When the power supply switches(turns on/off),you can see there is a period where the voltage(yellow)and current(green)cross,which is where you will see the most power
31、lost(purple).The quicker the voltage and current switch during that time,the less power you will lose.Note:Measuring losses during the conduction phase requires you to measure very low-level voltages,so its crucial to make sure your oscilloscope and probe offset are calibrated.Minimize power loss by
32、 analyzing switch-on or switch-off.How to Get Clean DC Power|8DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionOnce the device is fully turned on and reaches the conduction phase,youll see a spike in the power waveform that slowly drops back to 0 W.This is the instantaneous
33、power loss.By integrating the instantaneous power loss,you can tell how much power you are losing per switching cycle.Using this data,you can tweak design components to improve your devices efficiency.One of the key contributors to total efficiency is switching frequency.The more often you switch,th
34、e more power you lose.So,one common goal is to minimize the switchingfrequency.Math functions allow you to visualize something you wouldnt normally be able to see on an oscilloscope,like power loss.How to Get Clean DC Power|9Want to Learn More?See how this works in Evaluating Switching Power&Energy
35、Losses.DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionOutput power analysisNext,verify the quality of your output power.The DC output signal of your power supply may have unwanted AC ripple and noise,known as“periodic and random deviations”(PARD).While most supplies have s
36、ome internal filtering and regulation,there will always be some level of PARD.If the PARD is outside of your power-consuming devices spec,it can cause troublesome and elusive errors.It is really important to specify the PARD value in both the RMS and peak-to-peak values.The peak-to-peak value provid
37、es information for high magnitude,short duration noise spikes.This helps you identify any dangerously large spikes that could cause damage or accelerated component aging.The RMS value is the same as standard deviation,or uncertainty,and is used to characterize random noise.This helps you identify th
38、e overall stability and cleanness of your power.Analyzing PARD allows you to test the performance and quality of the supplys ability to reject switching noise and other noise sources.You can alter your design to meet your devices ripple and noisespecs.Figure 1.6.Measuring ripple on the DC output sig
39、nal in both RMS and peak-to-peak values.While most supplies have some internal filtering and regulation,there will always be some level of PARD.How to Get Clean DC Power|10Want to Learn More?Understand the details of output analysis and how to do it on an oscilloscope in the Switch Mode Power Supply
40、 application note.DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionEfficiency analysisTesting the efficiency of a power supply is important to tell you how well your supply performs.The efficiency is the ratio of the total output power to the total input power.If the efficie
41、ncy is outside of the typical range for that specific power supply technology,there is likely a design flaw that needs to be addressed.Additionally,all of the power consumed by your supply turns into heat.The higher your supplys efficiency,the cooler it will be.Efficiency is discussed in more depth
42、in the DC-DC conversionchapter.Power sequencingWhile analyzing the DC output,you should also look at the turn-on/off timings.When a device turns on or off,there is a certain sequence of events needed to output the voltage properly.One error often found in switching power supplies is undesirable even
43、ts occurring during the turn on/off period,like a rush of voltage,which is caused by the feedback loop trying to compensate for a lower voltage.This causes current spikes that can destroy the switching transistor in your device,drastically reducing a supplys lifespan.To prevent this from happening,c
44、onsider adding circuitry that will limit the on-time of switching transistors during startup.By analyzing the startup time on an oscilloscope,you can see if there are any current spikes occurring during startup,and then adjust your startup delay ifneeded.Consider adding circuitry that will limit the
45、 on-time of switching transistors during startup.How to Get Clean DC Power|11DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionFrequency response analysisThe last step of analyzing a power supply is evaluating its frequency response.Your device will react differently with var
46、ious input frequencies;known as“frequency response.”If you see abnormalities in the frequency response,you can use an FFT to target that specific frequency and determine whats causing it.These abnormalities or glitches could be causing problems in yoursupply.This analysis is often an entirely separa
47、te process that requires a network analyzer.But,if youre using a Keysight InfiniiVision oscilloscope,you can use the built-in frequency response analysis capability and wont need to use other equipment.To measure frequency response,supply a series of frequencies to your device and measure the gain a
48、nd phase of the devices output.Your measurements will give you a plot of gain and phase vs.frequency,known as a Bode plot.The oscilloscopes built-in frequency response analyzer supplies and measures the voltage at the input and output.Then it computes the gain at each frequency and adds it to the Bo
49、de plot.The gain is measured with this formula:Gain=20Log(VOUT/VIN).If you see abnormalities in the frequency response,use an FFT to target that specific frequency.Bode plots are typically used to analyze amplifiers and filters.Since a power supply is essentially an amplifier that has a negative fee
50、dback control loop(it amplifies the AC signal to respond to changes in the output load conditions),its easiest to analyze control loop response using a Bode plot.To perform a control loop response measurement,probe the AC voltage as the input and the DC output voltage as the output.This will help yo
51、u characterize the stability of your power supplydesign.Figure 1.7.Bode plot illustrating how the device under test responds to various frequencies.How to Get Clean DC Power|12Want to Learn More?To learn more about making control loop response measurements on an oscilloscope,watch the videoWant to L
52、earn More?To learn more about making control loop response measurements on an oscilloscope,read the application note.DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionWhats next?The first step to achieving clean power is to make sure you are efficiently converting your power
53、from AC to DC.To test this conversion,we covered methods for verifying input power,analyzing switching loss,verifying the output power,testing how well the supply performs and analyzing how your device will handle different frequencies.Now that weve tested the AC-DC power conversion components of yo
54、ur device,lets discuss how to turn unregulated DC voltage into regulated DC voltage.How to Get Clean DC Power|13DC-DC Power ConversionTesting Your Device ConclusionAC-DC Power ConversionDC to DC Power ConversionSTAGE 2How to Get Clean DC Power|14AC-DC Power ConversionTesting Your Device ConclusionDC
55、-DC Power ConversionSTAGE 2DC-DC Power ConversionJust like AC-DC conversion is a common power-producing component of an electrical device,DC-DC conversion is crucial for device performance and stability.Switch-mode DC-DC converters are common in electronic equipment because an ACDC converter does no
56、t always provide all the DC voltage levels required by your device.A DC-DC converter converts DC power from an unregulated source into a regulated voltage supply.Then the regulated voltage supply provides a steady voltage supply regardless of the load variations.As modern MPUs,FPGAs,and ASICs move t
57、oward faster operating speeds and lower operating voltages,your DC-DC converter designs must be able to handle fast-changing loads,maintain stable voltages and consume less power than ever before.Thats a tall order,but its notimpossible.This chapter will cover the common tests you should run to make
58、 sure your DC-DC designs meet your design parameters:Line regulation test Ripple test Efficiency test Load regulation test Start-up time testTheres a wide variety of equipment for testing DC-DC converters;well also briefly explore industry-standard test tools.How to Get Clean DC Power|15AC-DC Power
59、ConversionTesting Your Device ConclusionDC-DC Power ConversionSwitch mode DC-DC converter testsTo verify your DC-DC converters performance,you need to be able to make good measurements.And to make good measurements,you first need a good test setup.In general,you need both a power source and a load t
60、o test your DC-DC converter.The power source supplies power to your DC-DC converter while a load draws power from it.Most engineers use an electronic load,which allows you to vary the amount of power drawn from the converter.With this basic setup,you can measure the voltage and current across the in
61、put(VIN and IIN,respectively)and output(VOUT and IOUT,respectively).From these values,we can calculate the input power(PIN)and the output power(POUT).Depending on the test,input and output voltage and current can be measured using digital multimeters(DMMs),oscilloscopes,spectrum analyzers or power a
62、nalyzers.You need both a power source and a load to test your dc-dc converter.IinVinVoutIout+-DUTDC/DCconverterAAVVFigure 2.1.DC-DC converter test connection.How to Get Clean DC Power|16AC-DC Power ConversionTesting Your Device ConclusionDC-DC Power ConversionLine regulation testThe main function of
63、 the DC-DC converter is to convert an unstable power supply source into a source with stable voltage.This is known as“line regulation.”Line regulation is the DC-DC converters ability to sustain the specified output voltage while the input voltage changes.This is different from load regulation,which
64、well talk about later.You can use a line regulation test to see how well your converter handles various DC input voltages.To carry out this test,slowly vary the input voltage between your converters specified minimum and maximum voltage values.Simultaneously measure the output voltage.If your conver
65、ter works as expected,the output voltage changes should be within your specifications.Figure 2.2 shows the results of the line regulation test of a 15V DC-DC converter while the input voltage is swept from 2V to 12V.Note that the DC-DC converter starts to output 15V once the input voltage reaches th
66、e specified input voltage requirement(6V).Line regulation is the dc-dc converters ability to sustain the specified output voltage while the input voltage changes.Figure 2.2.Line regulation test results of a 15V DC-DC converter.Output voltage vs input voltage line regulationInput voltage(V)Output vol
67、tage(V)2.000.002.004.006.008.0010.0012.0014.0016.003.004.00 5.006.007.008.009.00 10.00 11.00 12.00Testing line regulation is important because it verifies your converter will be able provide the desired output voltage under all anticipated input voltage fluctuations.How to Get Clean DC Power|17AC-DC
68、 Power ConversionTesting Your Device ConclusionDC-DC Power ConversionRipple testThe ripple test is similar to the line regulation test,but a ripple test checks how your converter handles AC inputs.Remember that a DC-DC converter has to provide a stable power supply from an unstable power source.So,t
69、he DC-DC converter must filter out voltage ripples from an incoming power source.Use a ripple test to see how well your DC-DC converter rejects ripples from the incoming power supply(VIN).To perform a ripple test,power your converter with a DC voltage containing a small ripple,as shown in Figure 2.3
70、.There are several ways to create an input with ripple.One is to create a sine wave using a function generator and mix this signal with a power supplys output.Some power supplies have analog inputs that let you add external signals from a function generator into the DC output.Another way to create r
71、ipple is to use a power supply that has a builtin function generator,like the Keysight N6705C DC power analyzer.With the electronic load set to constant current mode,measure the output voltage of your DC-DC converter using an oscilloscope.You will usually see some amount ripple riding on top of the
72、DC voltage output.This is your output ripple.Using a spectrum analyzer,you could also detect the various frequency components of your output ripple.If you have high frequency ripples,these are most likely coming from your converters internal switching architecture.Its also worth noting that DC-DC co
73、nverters will always have some ripple on their output caused by their internal switching frequencies and other internal topologies.Its important to make sure your device can handle ripple from inside your converter and ripple caused by an unstablesource.Use a ripple test to see how well your dc-dc c
74、onverter rejects ripples from the incoming power supply(Vin).Its important to make sure your device can handle ripple from inside your converter and ripple caused by an unstablesource.Figure 2.3a.N6705A being set up to generate a 500mVpp ripple on a 9V output.Figure 2.3b.N6705C output on an oscillos
75、cope.How to Get Clean DC Power|18AC-DC Power ConversionTesting Your Device ConclusionDC-DC Power ConversionEfficiency testTypically,the most important test for a DC-DC converter is efficiency.This is especially true for battery-powered devices because efficiency directly impacts battery life.The eff
76、iciency of the converter is the ratio between the output power and the inputpower.To test efficiency,use a DC power supply to provide power to the converter and an electronic load to draw power from the converter.The efficiency of a DC-DC converter design is usually affected by the input voltage and
77、 the amount of power consumed by the load.Figure 2.4 shows the efficiency vs.load current at various input voltages(6V,9V and 12V).The electronic load was configured to sweep through a load current from 0 to 10 mA.As you can see,the converters efficiency increases as the load draws more power.Effici
78、ency will fall when power draw nears the converters output power limit.So when youre choosing a DC-DC converter design,make sure to design just enough power headroom to manage yourload.The efficiency of the converter is the ratio between the output power and the input power.Your converters efficienc
79、y is the cornerstone of your products battery life.It will help determine the weight,battery life and feature set you can squeeze into your device.Figure 2.4.Efficiency test results under varying load currents.Eficiency vs load currentEficiency%Load current(mA)52.0%32.5%23.6%22.2%20.5%19.0%17.9%15.9
80、%14.3%12.5%10.2%6.7%32.1%31.4%30.7%29.9%28.6%26.6%23.7%19.4%17.6%51.8%51.6%50.8%50.4%49.4%47.9%46.1%42.8%34.8%1.002.003.004.005.006.007.008.009.0010.00Vin=12VVin=9VVin=6VHow to Get Clean DC Power|19AC-DC Power ConversionTesting Your Device ConclusionDC-DC Power ConversionLoad regulation testLoad reg
81、ulation test measures the ability of a DC-DC converter to sustain its specified output voltage under varying load currents.To perform this test,use an electronic load to vary the output load between your specified minimum and maximum load current values.While the electronic load pulls different amou
82、nts of power from your DC-DC converter,the output voltage should remain within your design specs.The load regulation test measures the ability of a dc-dc converter to sustain its specified output voltage under varying load currents.Figure 2.5 shows load regulation test results.Note that the DC-DC co
83、nverter fails to maintain its output voltage of 15V as the power draw exceeds its maximum power output capability.The output voltage may fluctuate when more power is pulled from your DC-DC converter.This is especially true as your converter starts to heat up from more power dissipation.Its important
84、 to make sure your converters voltage output remains within specifications in its power envelope.Figure 2.5.Load regulation test result under varying load currents.Output voltage vs load current load regulationOutput voltage(V)Load current(mA)00.002.004.006.008.0010.0012.0014.0016.0010.020.030.040.0
85、50.060.070.080.0 90.00How to Get Clean DC Power|20AC-DC Power ConversionTesting Your Device ConclusionDC-DC Power ConversionStart-up time testThe start-up time test measures the time delay between when the input voltage is applied to the DC-DC converter and when its output voltage stabilizes.For thi
86、s test,connect one oscilloscope channel across the input of the DC-DC converter and a second channel to the output of the DC-DC converter.Set the oscilloscope to trigger when input voltage is applied to the DC-DC converter.Figure 2.6 shows a typical result of this test.Start-up time is important as
87、modern MPUs,FPGAs,ASICs,etc.have start-up voltage sequence requirements for input voltages.Failing to adhere to a devices start-up voltage sequence will cause boot up failure or even permanent device damage.Power sequencing will be explored further in the next chapter.Start-up time is important as m
88、odern MPUs,FPGAs,ASICs,etc.have start-up voltage sequence requirements for input voltages.Figure 2.6.BenchVue start-up time test and capture setup.How to Get Clean DC Power|21AC-DC Power ConversionTesting Your Device ConclusionDC-DC Power ConversionEquipment required for DC-DC converter testingTesti
89、ng the DC-DC converter is a process that usually requires several different instruments.To explore timing characteristics,you need an oscilloscope.To explore potentially harmful frequency components,you need a spectrum analyzer.For ripple testing,youll need both a DC power supply and a function gene
90、rator.These are all commonly used tools for this type of testing,but it can be difficult to coordinate this much equipment.Often,youll also need to write code to synchronize these instruments,which can be complicated and time consuming.If you regularly face the challenge of trying to coordinate mult
91、iple instruments while testing power,you might want to consider a solution many engineers turn to:an all-in-one power analyzer like the N6705C DC power Analyzer.Its flexible configurations allow you to combine power supply,oscilloscope,and function generator capabilities into one box,so you can skip
92、 equipment setup and get right to testing and verifying your power designs.Whats next?DC-DC converters play a major role in modern electronics.They must be a source of stable and reliable power supply while consuming as little power as possible.The basic functions of a DC-DC converter are covered by
93、 the line regulation test,ripple test and load regulation test.The efficiency test ensures that your DC-DC converter is performing its job without consuming too much power,and the tight start-up voltage sequence demanded by modern ICs is covered by the start-up time test.Now that weve looked at both
94、 AC-DC and DC-DC power-producing components of a device,its time to look more closely at how to test and protect your power-consuming device.How to Get Clean DC Power|22Want to Learn More?Learn more about designing and testing DC-DC converters in the Evaluating DC-DC Converters and PDN application n
95、ote.AC-DC Power ConversionTesting Your Device ConclusionDC-DC Power ConversionTesting and Protecting Your Power Consuming DeviceSTAGE 3How to Get Clean DC Power|23AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device CHAPTER 3Testing and Protecting Your Power-Consuming DeviceThis
96、 chapter explores four main considerations you should think about when testing your power-consuming device:Device current measurement techniques.Seamlessly measuring current is a crucial step for evaluating battery life and device power management.Power sequencing techniques and considerations.Impro
97、per sequencing can cause significant performance issues and device damage.Two easy ways you can protect your device from accidental damage during testing.Best practices for analyzing and minimizing PARD.How to Get Clean DC Power|24AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your De
98、vice Device current measurement techniquesLow-power devices like wearables,portable medical devices and smart phones consume power at highly variable ratesfrom microseconds to seconds and picoamperes to amperes.Accurate power analysis is critical to design a device with a long battery life.For highl
99、y-accurate power analysis,you need fast and accurate measurement results that properly characterize battery drain.Measuring dynamic current drainTo save energy in battery-powered devices like wireless sensors,you need to design your devices sub-circuits to be active only whennecessary.Most of the ti
100、me,the device is in a sleep mode with minimum current drain and only the real-time clock is operating.The device wakes up periodically to perform measurements and transmit data to a receiving node.To optimize battery life,you should characterize performance and understand the devices energy requirem
101、ents in each mode.This can be difficult since each operating mode has its own range of current draw which are often very different,from sub-A during sleep mode to 100 mA during transmit mode.Table 1.Typical sensor current levels and time at those levels during measurement,transmission and sleep.Mode
102、CurrentDurationTransmission(TX)20-100 mA1-100 msActive100 A-10 mA10-100 msSleep500 nA-50 A100 ms-minuteThe main challenge in measuring the current consumption of these devices is the current signals wide dynamic range.The main challenge in measuring the current consumption of these devices is the cu
103、rrent signals wide dynamic range.A mobile device typically switches back and forth between active states,where it draws very high and fast peak currents,and an idle or standby current mode,where it draws very small DC and AC currents.Figure 3.1 shows the current drain measured on a GSM cell phone wh
104、en making a call.The active current peaks as high as 2 A,but in idle mode the current drain is extremely small.Typically,this signal would be very hard to measureaccurately.Figure 3.1.The current drain measured on a GSM cell phone when making a call.00.002-0.0020.004-0.0040.006-0.0060.008000-0.0080.
105、010-0.010F1-A-1121Transmit current pulsesReceive current pulsesIdle current500 mA/div2 ms/divHow to Get Clean DC Power|25AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Seamless current measurementsBecause traditional equipment has a difficult time measuring signals with su
106、ch a wide dynamic range,designers often turn to source/measure units(SMUs).SMUs are known for having very high accuracy for both sourcing and measuring current.However,conventional SMUs are not ideal for sourcing and measuring battery-powered devices and their components.They often lack the voltage
107、transient response needed to hold a stable output.Even though they offer very accurate measurements over a fixed range,they lack the ability to change ranges quickly and without disrupting their measurements.These disruptions can cause you to miss crucial moments of your devices power draw or sacrif
108、ice accuracy at other ranges.To avoid these issues,make sure to use an SMU with seamless ranging when measuring wide-dynamic range devices.Seamless ranging allows you to transition from one current measurement range to another without glitches or discontinuities in the power output.This is essential
109、 for power and battery optimization measurements on devices with various standby(low current)and transmit(high current)cycles.Figure 3.2 shows a graphical representation of using seamless ranging to measure dynamic current.Seamless ranging allows you to transition from one current measurement range
110、to another without glitches or discontinuities in the power output.Figure 3.2.Seamless ranging to measure dynamic current.Seamless current measurement200 kHz,18-bit digitizer acts like single range of 30-bitsSeamless range changesTransmit mode(0.03%+200 A)MeasurementaccuracyRange3A100 mA+-(0.025%+7
111、A)1 mA(0.025%+80 nA)10 AFixed range(0.025%+8 nA)=Seamless range changeStandby modeSleep modeHow to Get Clean DC Power|26AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Properly sequence multiple power inputs to protect your deviceMost devices have multiple DC inputs,which m
112、ay be sensitive to the order in which the inputs turn on or off.An uncontrolled sequence could cause latch-up,or excessive current to flow,resulting in compromised reliability or even immediate catastrophic failure.So,properly sequencing multiple voltages at turn-on and turn-off is essential for per
113、formance andreliability.Properly sequencing multiple voltages at turn-on and turn-off is essential for performance and reliability.There are a few methods for protecting against improperly sequenced power inputs:1.Diodes can be placed from one input to another to clamp the voltages,thereby preventin
114、g one input voltage from going too far above or below another input voltage.But,this method has limited effectiveness and mixed resultsits not recommended.2.Relays can be put in series with each input and controlled with timing circuitry,but the relays introduce variable series impedance and timings
115、 are often imprecise.Relays also add additional cost so use these only when necessary.3.FETs with associated control circuitry can be placed in series with each input.However this method requires significant design time and adds design complexity.4.Multiple DC power supplies can be controlled throug
116、h software,but once again,timing is imprecise and response times can be slow.The preferred method is to use a power supply system that has output sequencing integrated into the system itself.This method is the most precise and introduces the fewest complications.Many systems offer the ability to pre
117、cisely control the turn-on and turn-off sequence of multiple outputs.However,when testing your device,an industry best-practice is to use a lab power supply in place of the power supply that will ultimately be part of your design.This way,you can verify your power supply using the tests from Chapter
118、2 and verify your device using tips from this chapter.This makes it much easier for you to isolate elusive errors or performance issues.To power your device,you need a lab power supply that can emulate your systems final power supply.This means a power supply that can set timings with sub-millisecon
119、d resolution.Synchronization across lab power supply systems is also helpful if you need to emulate a large number of device inputs.How to Get Clean DC Power|27AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Figure 3.3 shows a simple example of a turn-on sequence test using
120、 a Keysight N6705C power analyzer.The sequencing is controlled by setting different turn-on delay times for each of the outputs.When all outputs are told to turn on simultaneously,the delays get automatically activated,resulting in a sequenced turn on.In this case,the power analyzer is emulating a 4
121、-output power supply.There are four power supply outputs supplying voltages of 10 V,7.5 V,5 V,and 3.3 V as well as delays set to 5 ms,10 ms,15ms,and 20 ms.For further testing,you could also set the output voltage rise time(slew rate)independently for each output.Figure 3.4 shows the actual signal ou
122、tputs on the power analyzers built-inoscilloscope.By controlling the power sequencing for your device,you can test your devices performance under non-ideal conditions.This helps you identify any potential risks and select the right power supply for your device.Figure 3.3.N6705C delay times are simpl
123、e to set and facilitate precise output voltage turn-on sequencing.Figure 3.4.N6705Cs built-in oscilloscope shows outputs turning on precisely according to the set delay times.The preferred method is to use a power supply system that has output sequencing integrated into the systemitself.How to Get C
124、lean DC Power|28AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device How to protect your device when testing with a power supplyThe primary causes of device failure are over-voltage and over-current events.Sometimes these are a very short duration while others last until they ar
125、e discovered.In either case,over-voltage and over-current events are dangerous.Controlling the current and voltage outputs of your power supply allows you to avoid overstressing your DUT under fault or near-fault conditions.Over-voltage or over-current events can occur for many reasons,including:Int
126、ernal circuit failures that cause the output voltage to rise Device controller failure or programming error Improperly using more than one power source,such as another power supply or battery Having an open sense-lead connection Using local voltage sensing instead of remote sensing Countering an ove
127、r-voltage condition by shorting the power-supply output terminals.This leads to a discharging current surge from the device Large device inrush currentMost DC power supplies have features that protect your devices from potentially damaging voltage or current levels.These are known as over-voltage pr
128、otection and over-current protection.When your device trips a protection circuit in a power supply,the protection circuit turns off its output and displays a warning.When testing,it is important to understand and use these protection features.The primary causes of device failure are over-voltage and
129、 over-current events.Most dc power supplies have features that protect your devices from potentially damaging voltage or current levels.Excessive current caused by overloading of the device Excessive current related to imminent or actual device circuit failure Test system wiring short circuitHow to
130、Get Clean DC Power|29AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Over-voltage protectionOver-voltage protection(OVP)is a value set in volts designed to protect your device from excessive voltage.When the power supply output voltage exceeds your OVP setting,the protectio
131、n will trip and turn off the output.Power supplies always have OVP turned on by default,but it is typically set well above the maximum rated output of the power supply.To protect your device,set your OVP level low enough to avoid excessive voltage but high enough to prevent“nuisance tripping”from no
132、rmal fluctuations.Fluctuations often occur during output transient conditions,such as load current changes.OVP circuits respond to an over-voltage condition in microseconds;however,the output voltage itself wont go down immediately.The outputs fall time depends on the downprogramming capabilities of
133、 the power supply and the load that is connected to the output.Some power supplies have a silicon-controlled rectifier(SCR)across the output that fires when the OVP trips,which allows for a much faster fall time.Figure 3.5.An over-voltage warning in the lower left indicating that OVP was tripped.How
134、 to Get Clean DC Power|30Want to Learn More?Learn more about over-voltage protection and how to use it in the Over-Voltage Protection in Power Supplies application note.AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Over-current protectionOver-current protection(OCP)circui
135、ts protect your device from excessive current.The current limit setting determines the value in amps at which the power supply will prevent excessive current from flowing.This is different from constant current(CC)mode,which regulates the output current at the current limit but will not turn off the
136、 output completely.Instead,in constant current mode,the voltage will decrease below your specified voltage setting and the power supply will continue to produce current at the CC setting.Figure 3.6.An over-current warning in the lower left indicating that OCP was tripped.Over-current protection(OCP)
137、circuits protect your device from excessive current.OCP completely shuts off the output to prevent excessive current flow into your device.When you enable OCP and the supply enters CC mode,a protection circuit will trip and turn off the output.Effectively,OCP turns the current limit setting into a t
138、rip value.Make sure to set your current limit low enough to protect your DUT from excessive current but high enough to prevent nuisance tripping due to normal fluctuations in the output current.These fluctuations often occur during output transient conditions,such as during an output voltage change.
139、Unlike OVP,OCP is turned off by default.How to Get Clean DC Power|31AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Periodic and random deviation(PARD)PARD(often known as ripple and noise)is the periodic and random deviation of a DC output voltage from its average value ove
140、r a specified bandwidth with all other parameters held constant.It is representative of all undesirable AC and noise components that remain in the DC output voltage after the regulation and filtering circuitry(see Figure 3.7).PARD can be measured in both RMS and peak-to-peak values and is typically
141、specified over a bandwidth range of 20 Hz to 20 MHz.Any deviation below 20 Hz is included in a specification called output drift.PARD(often known as ripple and noise)is the periodic and random deviation of a dc output voltage from its average value In many applications,a low output ripple specificat
142、ion is critical for device performance.Take,for example,a power supply providing power to a high gain amplifier with inadequate ripple rejection.A portion of the power supplys PARD will be amplified along with the desired signal.This could cause any number of errors in your device.VOUTdcOUTPUTPARDTi
143、meFigure 3.7.PARD consists of undesirable signals superimposed on the DC output of a power supply.It is also important to measure the PARD value as both a peak-to-peak value and an RMS value.The peak-to-peak value provides information on high magnitude,short duration noise spikes while the RMS value
144、 helps you determine your expected signal-to-noise ratio.While some amount of PARD is unavoidable,its helpful to eliminate it as much as possible during the design process.How to Get Clean DC Power|32AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Eliminate noise from low-l
145、evel measurementsNoise in low-level measurements can come from different sources,and its much easier to eliminate noise than to filter it.When making low-level measurements,work to eliminate noise from the following sources:Power supply noiseStarting with a low-noise supply is a great way to keep no
146、ise out of your measurements.Linear power supplies have lower common-mode noise currents and generally operate at low frequency.However,you can use switch-mode supplies successfully if their specifications include a low common-mode current.As a rule of thumb,common-mode current over 20-30 mA is like
147、ly to cause trouble.As a rule of thumb,common-mode current over 20-30 ma is likely to cause trouble.DUT to power supply connectionsMinimize conducted noise by eliminating ground loops.Ideally,there should be only one connection to ground.In rack systems,where multiple ground points are inevitable,se
148、parate the DC distribution path from other conductive paths that carry ground currents.If necessary,float the power supply(dont connect either terminal directly to ground).Minimize radiated pick-up(both electric and magnetic)by using twisted shielded conductors for the output and remote sense leads.
149、To make sure the shield doesnt carry current,connect the shield to ground at one end only,preferably the single-point ground on the supply(Figure 3.8).ShieldCShield+S-S+-LoadPowerSupplyFigure 3.8.Minimizing radiated pick-up with twisted shield leads for both output and remote sense leads.How to Get
150、Clean DC Power|33AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Figure 3.9.A set of shielded twisted pair(STP).Minimize the power supplys common-mode noise current by equalizing the impedance to ground from the plus and minus output terminals.Also,equalize the DUTs impedan
151、ce to ground from the plus and minus input terminals.Both magnetic coupling and capacitive leakage provide a return path for noisy ground loop current at higher frequencies.To balance your DUTs impedance to ground for your test frequencies,use a common-mode choke in series with the output leads and
152、a shunt capacitor from each lead toground.Current variations to the DUTRapid changes in the DUTs current demand will cause voltage spikes.To prevent this,add a bypass capacitor close to the load.The capacitor should have a low impedance at the highest testing frequencies.Avoid imbalances in load lea
153、d inductance;direct connections to the DUT,such as twisted shielded pair,are your bestbet.How to Get Clean DC Power|34AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device Whats nextFor your designs to be effective and efficient,you must ensure both your power producing and power
154、 consuming blocks are functioning properly.In this chapter,we looked at four key areas that help you protect and characterize your power consuming devices.Now that weve looked at how to test and protect your power consuming devices,lets some of the solutions available to help you get cleanpower.How
155、to Get Clean DC Power|35AC-DC Power ConversionDC-DC Power ConversionConclusionTesting Your Device ConclusionCHAPTER 4How to Get Clean DC Power|36AC-DC Power ConversionDC-DC Power ConversionTesting Your Device ConclusionCHAPTER 4ConclusionClean DC powerClean power is the key to improving the performa
156、nce and reliability of your devices.To help you find and eliminate noise in your system and achieve clean power,weve outlined the three stages outlined in this guide.Test the effectiveness and efficiency of your AC to DC converter by analyzing the key power supply attributes outlined in Chapter 1.Sa
157、ve testing time with the automation available in modern tools and move to the next stage of testing faster.Refer to Chapter 2 for tips on how to effectively test your DC-DC converter.Stabilize your device by meeting ripple and noise tolerances.Eliminate noise,so your DC-DC converter can handle fast
158、changing loads,maintain stable voltages and consume less power.Mitigating ripple and noise is important,but no power supply is perfectly clean.Its important to test how your device handles non-ideal power.Avoid damaging your device with the steps found in Chapter 3.Remember,its much easier to elimin
159、ate noise than to filter it.So use this guides practical tips to find and eliminate more noise in your system and youll be on your way to clean DC power.To stay up to date with the industrys most recent tutorials,techniques,and best practices check out the Keysight Labs YouTube channel,follow the Ke
160、ysight Bench Facebook Page,and subscribe to our blog.How to Get Clean DC Power|37Want to Learn More?Learn more about power supply and power testing solutions.AC-DC Power ConversionDC-DC Power ConversionTesting Your Device ConclusionN6705C power analyzers:Gain insights in minuteswith no programming r
161、equired The N6705C DC Power Analyzer provides unrivaled productivity gains when sourcing and measuring DC voltage and current into a DUT.The N6705C is a highly integrated instrument that combines up to four advanced DC power supplies,DMM,oscilloscope,arbitrary waveform generator and datalogger.It pr
162、ovides an easy-to-use interface,with all sourcing and measuring functions available from the front panel.The N6705C makes it easy to:Set up and view critical turn-on/turn-off sequences Measure and display voltage,current versus time to visualize power into the DUT Control DC bias supply ramp-up/down
163、 rates Generate DC bias supply transients and disturbances Log data for seconds,minutes,hours,or even days to see current consumption or capture anomalies Save data and screen shots to internal storage or external USB memory devices Save and name your setup and tests for easy re-use Share setups wit
164、h colleaguesHow to Get Clean DC Power|38Want to Learn More?Learn more about Keysight power analyzersAC-DC Power ConversionDC-DC Power ConversionTesting Your Device ConclusionOscilloscopesKeysight InfiniiVision 3000,4000 and 6000 X-Series oscilloscopes offer integrated power measurement and analysis
165、options for a quick and easy way to analyze the reliability,efficiency and performance of your switching and linear power supplies.These applications include:Input measurements Power quality:real power,apparent power,reactive power,power factor,crest factor(V&I),phase angle Current harmonics(based o
166、n IEC 61000-3-2 up to the 40th harmonic)Inrush currentSwitching measurements Rds-on&Vce-sat Switching loss(power&energy)Slew rate(dv/dt&di/dt)Modulation(duty cycle,pulse-width,period,frequency,etc.,versus time plot)Output measurements Output ripple Turn-on/turn-off time Transient response time Effic
167、iencyHow to Get Clean DC Power|39Want to Learn More?Learn tips to improve your power testing with oscilloscopes or more about the Keysight oscilloscope power measurement options.AC-DC Power ConversionDC-DC Power ConversionTesting Your Device ConclusionPower supplies:Power to advance your testOur bro
168、ad selection of bench-friendly and system-ready instruments can help you overcome your testing challengesfrom basic to complexwith a wealth of available capabilities.Test confidently with clean,precise DC power thats fully specified and guaranteed Safeguard loads from potential harm with robust outp
169、ut protection and fault detection capabilities Enhance system flexibility with built-in,DMM-quality measurement functionsHow to Get Clean DC Power|40Want to Learn More?See all the power supply options with more than 50 new models.AC-DC Power ConversionDC-DC Power ConversionTesting Your Device Conclu
170、sionThis information is subject to change without notice.Keysight Technologies,2017 2023,Published in USA,March 15,2023,5992-2717.ENKeysight enables innovators to push the boundaries of engineering by quickly solving design,emulation,and test challenges to create the best product experiences.Start your innovation journey at .