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PCB design must master: switching power supply ripple measurement method

One of the most critical indicators of switching regulators is ripple, which is mainly caused by the way the switch is switched. It also affects the operation of subsequent circuits due to the presence of ripple, especially in the case of ripple sensitive. How to correctly measure switching power supply ripple? How to effectively suppress the ripple of the switching power supply to meet the requirements of the power supply circuit? These are all important skills that PCB design engineers need to master.




Switching power supply ripple measurement

To effectively reduce the output ripple of the switching power supply, we must first have a more reliable test method. The false waveform caused by the problem of the test method is not correct.

Basic requirements: AC oscilloscope AC coupling, 20MHz bandwidth limit, unplug the probe ground

1, AC coupling is to remove the superimposed DC voltage to get an accurate waveform.




2, open the 20MHz bandwidth limit is to prevent high-frequency noise interference, to prevent the detection of erroneous results. Because the high frequency component has a large amplitude, it should be removed when measuring.

3. Unplug the grounding clamp of the oscilloscope probe and measure it with a grounding ring to reduce interference. Many departments do not have a grounding ring and measure directly with the grounding clamp of the probe if the error allows. However, this factor should be considered when judging eligibility.




Another point is to use a 50Ω terminal. According to the Yokogawa oscilloscope, the 50Ω module removes the DC component and accurately measures the AC component. However, few oscilloscopes are equipped with this special probe. In most cases, the probe is measured with a standard 100KΩ to 10MΩ, and the impact is temporarily unclear.

The above is a basic precaution when measuring switch ripple. If the oscilloscope probe is not in direct contact with the output point, it should be measured with twisted pair or 50Ω coaxial cable.

When measuring high frequency noise, use the oscilloscope's full passband, typically on the order of hundreds of megahertz to GHz. Others are the same as above.

Different companies may have different test methods. In the final analysis, you must be clear about your test results. The second is to be recognized by the customer.

About oscilloscope

Some digital oscilloscopes cannot properly measure ripple due to interference and memory depth. Replace the oscilloscope at this time. In this respect, although the old analog oscilloscope has a bandwidth of only a few tens of megabytes, it performs better than a digital oscilloscope.