The Application of SDS2000 in the Analysis of Switching Power Supply

Power supply is an indispensable part of all electronic products. Power supplies are divided into switching power supplies and linear power supplies. Among them, switching power supplies have become the mainstream architecture of power supplies in digital computing and network communication systems. The quality of the switching power supply is related to the overall performance of the product. Therefore, it is particularly important to analyze the power supply in R&D and production testing. The SDS2000 super fluorescent oscilloscope launched by SIGLENT is equipped with a powerful power analysis module, which supports the test and measurement of most power performance indicators. The following will introduce the power analysis function of SDS2000 in detail by analyzing the input module of the power board.

Take the power demo version STBX as an example, its physical view is shown in Figure 1:



Figure 1 STBX

STBX circuit schematic diagram is shown in Figure 2:



Figure 2 Schematic diagram

Before operating, first check whether the oscilloscope and power demo board are working well, and start power analysis after ensuring that the oscilloscope, power demo board and probes are all in good condition.

First of all, use SDS2304, differential probe, current probe to measure the waveform of the power input terminal and get the result as shown in the figure below (Figure 3). Among them, the purple-red curve of channel 2 represents the voltage waveform, and the green curve of channel 4 represents the current waveform. Through the powerful parameter measurement function of SDS2000, we can easily get the peak-to-peak value, effective value, value, value, etc. of current and voltage. The measurement items in the figure are the peak-to-peak value and frequency of current and voltage.



Figure 3 Input primary signal

Since each specific voltage and current probe has a different transmission delay, the timing delay error between the voltage and current probes will have a great impact on the power measurement. Therefore, in order to perform the power measurement and calculation, we must use the "delay deviation correction" program to balance the time delay between the voltage and current probes in actual operation. This step is very important, and the measurement can be ensured by performing probe delay deviation correction before measuring the power.



Figure 4 Power analysis items

As shown in the figure above (Figure 4), SDS2000 is equipped with a powerful power analysis module. In the power analysis, you can choose power quality, current harmonics, inrush current, switching loss, conversion speed, modulation, output ripple, transient response, etc. Different analysis methods. This allows engineers to have more flexible choices and larger operating space in practical applications. This article will focus on power quality analysis, current harmonic analysis, and inrush current analysis.

Power quality analysis can measure important indicators of power quality such as power, phase angle, etc. Part of the AC current can flow into or out of the load without providing energy. This type of current is called reactive current or harmonic current, which can generate "apparent" power higher than actual power consumption. Power quality is measured by the following measured values: power factor, effective power, apparent power, reactive power, crest factor, current phase angle and AC line voltage, as shown in the figure below (Figure 5).



Figure 5 Analyzable parameters

The display interface of measurement parameters is as follows:



Figure 6 Power factor



Figure 7 Measurement items



Figure 8 Phase angle

As can be seen in Figure 6, Figure 7, and Figure 8 above, SDS2000 uses the MATH calculation function, combined with the powerful measurement statistics function, can easily obtain the many information we need, and can compare the current value, average value, and value of the measurement item. , Value, and standard deviation are displayed at the same time. Provide a more efficient and convenient experience for the majority of engineers.

Next, we have to analyze the current harmonics, select the current harmonics, set the signal frequency type to 50Hz, and select Class A as the standard. As follows:



Figure 9 Select current harmonic analysis



Figure 10 Setting signal frequency and current harmonic standard type

When we choose the current harmonic standard, we must first understand the difference between the standards.

Class A: suitable for balanced three-phase equipment, household appliances (except Class D equipment), tools (except portable tools), incandescent lamp dimmers and audio equipment;

Class B: suitable for portable tools;

Class C: Applicable to lighting equipment. When pressing the "Apply" soft key (in the "Power Application" main menu), Class C requires power factor calculation. Therefore, when "Power Application" is disabled, only Class C can be selected , Which will force you to press "Apply" again to perform the analysis;

Class D: Applicable to equipment with a rated power less than or equal to 600 W. The types are as follows: personal computers and personal computer monitors, TV receivers.

After the setting is completed, open the FFT operation function in MATH, select the Hanning window type, select the table display in the display, and press the "Apply" button. After the analysis is completed, the result of the current harmonic analysis can be obtained as shown in Figure 11:



Figure 11 Current harmonic analysis

It can be seen that the current table shows the 8th harmonic, the harmonic frequency is 50Hz~400Hz, and the current effective value (RMS), limit value (RMS), margin (Margin) and pass/fail status can also be observed. In the figure, the remaining amount of the harmonics corresponding to the frequency of 100Hz, 200Hz, 300Hz is less than 80%, and the statistics are Fail at this time, and the rest are Pass (Note: The calculation method of the margin is {(limit value-actual value)/limit value} *100%). In practical applications, more observable harmonics will bring better power supply parameter analysis.

SDS2000 inrush current analysis can measure the power inrush current and record the current waveform. The peak current can be positive or negative, so the result is the measured value or the larger one.

The measurement results are as follows (Figure 12):



Figure 12 Inrush current measurement

SDS2000, as a Dingyang super fluorescent oscilloscope adopting original SPO technology, is equipped with a powerful power analysis module while having high processing speed and powerful measurement and statistics functions. It is a sharp sword in power analysis and adds a number of measurement indicators. At the same time, it simplifies the operation and optimizes the interface, making it more convenient and efficient for engineers to use.

As a manufacturer of general-purpose instruments such as digital oscilloscopes integrating R&D, production, sales and service, SIGLENT has always focused on R&D and manufacturing of test and measurement instruments, insisting on R&D as its competitiveness, and through continuous technological innovation and strict quality control To deepen the brand building step by step, we have reason to believe that in the future SIGLENT will continue to bring more and more useful and practical products.