Datasheet

ManualsBrandsTEKTRONIX ManualsLaboratory Test EquipmentDigital 100 MHz 4-channel 2.5 null 10 null 11 Bit Digital storage (DSO), Mixed signal (MSO), Spectrum

Introduction

Power supplies can be found in many different electronic

devices, from children’s toys to computers and ofﬁce

equipment to industrial equipment. They are used to convert

electrical power from one form to another for proper device

operation. Common examples are AC-to-DC converters which

change AC voltages into regulated DC voltages or DC-to-DC

converters which convert battery power into required voltage

levels.

Power supplies range from traditional linear supplies to high

efﬁciency switch-mode power supplies (SMPS) designed for

complex, dynamic operating environments. The load on a

device can change dramatically from one instant to the next,

and even a commodity switch-mode power supply must be

able to withstand sudden peak loads that far exceed average

operating levels. Engineers designing power supplies or the

systems that use them need to understand their power supply’s

behavior under conditions ranging from quiescent to worst-case.

Power Supply Measurement and Analysis

with Bench Oscilloscopes

Application Note

What you will learn:

How to simplify power supplies analysis with maximum accuracy with the Tektronix MDO/MSO/

DPO4000 and MDO/MSO/DPO3000 Series.

Summary of content (14 pages)

PAGE 1
Power Supply Measurement and Analysis with Bench Oscilloscopes Application Note What you will learn: How to simplify power supplies analysis with maximum accuracy with the Tektronix MDO/MSO/ DPO4000 and MDO/MSO/DPO3000 Series. Introduction Power supplies can be found in many different electronic devices, from children’s toys to computers and office equipment to industrial equipment. They are used to convert electrical power from one form to another for proper device operation.
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Application Note Line Voltage Input Filter Switching Device Rectifier & Filter VOUT VIN Power Quality Harmonics Analysis Total Harmonic Distortion Switching Loss Safe Operating Area di/dt, dv/dt Output Voltage Ripple Control Circuit PWM Feedback Modulation Anaylsis Figure 1. SMPS Components that are Characterized with Power Analysis Software.
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Power Supply Measurement and Analysis with Bench Oscilloscopes 1 2 3 4 2 3 4 2 3 4 Sample Mode 1 2 3 4 1 2 3 4 1 2 3 4 Figure 2. Sample Mode. 1 Sample Mode Figure 3. Average Mode. 1 Sample Mode Figure 4. Hi Res Mode. Oscilloscope Acquisition Modes The oscilloscope’s acquisition modes control how electrical signals are sampled, processed, and displayed. The resulting waveform points are digital values that are stored in memory and displayed to construct the waveform.
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Application Note Figure 5. Default Timing Skew between Voltage and Current Probes. Figure 6. Nominal Correction of Timing Skew between Voltage and Current Probes. Eliminating Skew between Voltage and Current Probes Tektronix MDO/MSO/DPO4000 and MDO/MSO/DPO3000 Series oscilloscopes offer a “Deskew” feature to remove the skew between the probes.
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Power Supply Measurement and Analysis with Bench Oscilloscopes Figure 7. Tektronix Deskew Pulse Generator and Deskew Fixture. Figure 8. Manual Removal of Timing Skew between Voltage and Current Probes. The TEK-DPG provides a source signal to the Power Measurement Deskew Fixture (Tektronix part number 067-1686-XX) as shown in Figure 7. With the probes connected to the deskew fixture, the “Actual Deskew” may be manually dialed-in to change the deskew value to precisely align the waveforms.
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Application Note Bandwidth Limiting Filters Limiting the oscilloscope’s bandwidth removes noise or unwanted high frequency content from the displayed waveform, resulting in a cleaner signal. The MDO/MSO/ DPO4000 and MDO/MSO/DPO3000 Series offers built-in bandwidth limiting filters, as shown in Figure 10. In some cases, the probe may also be equipped with bandwidth limiting filters. Figure 10. Bandwidth Limiting Filters Available on an MSO/DPO4000B Series Oscilloscope with a TDP1000 Attached.
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Power Supply Measurement and Analysis with Bench Oscilloscopes Figure 11. Harmonics Analysis. Figure 12. Power Quality Measurements. Harmonics Performing harmonics analysis is as easy as taking an ordinary waveform measurement. Since the signal in this case is a repeating periodic waveform, it’s a simple matter to trigger and display it.
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Application Note Switching Loss Transistor switch circuits typically dissipate the most energy during transitions because circuit parasitics prevent the devices from switching instantaneously. The energy lost in a switching device, such as MOSFET or IGBT as it transitions from an OFF to ON state is defined as Turn-on loss. Similarly, Turn-off loss is the energy lost when the switching device transitions from an ON to OFF state.
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Power Supply Measurement and Analysis with Bench Oscilloscopes Figure 14. SOA Mask Testing. Figure 15. Slew Rate Measurements. The other major challenge is the high dynamic range required for accurate switching loss measurements. The voltage across the switching device changes dramatically between the On and Off states, making it difficult to accurately measure both states in a single acquisition.
PAGE 10
Application Note Modulation Analysis Figure 16. Modulation Analysis on an IGBT’s Gate Drive During Power-up. Output Analysis Ideally, the output of a DC power supply should not have any switching harmonics or other non-ideal noise components. Realistically, that is not possible. Output analysis measurements are essential to determine the effects of variations in input voltage or load on the output voltage. These measurements include: Modulation Analysis Ripple 10 www.tektronix.
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Power Supply Measurement and Analysis with Bench Oscilloscopes Conclusion The power supply is integral to virtually every type of linepowered and battery-operated electronic product, and the switch-mode power supply (SMPS) has become the dominant architecture in many applications. A single switch-mode power supply’s performance — or its failure — can affect the fate of a large, costly system. Figure 17. Ripple Measurements.
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Application Note Which oscilloscope is right for you? Tektronix Bench Oscilloscopes offer a range of models to meet your needs and your budget.
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Power Supply Measurement and Analysis with Bench Oscilloscopes www.tektronix.
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