How to Measure the Ripple of a Switching Power Supply?
A crucial indicator of a switch mode stabilized power supply is ripple, which is mainly caused by the switching mode and can affect the operation of subsequent circuits, especially in situations where ripple is sensitive. How to correctly measure the ripple of a switching power supply? How to effectively suppress the ripple of the switching power supply to meet the requirements of the power supply circuit? These are important skills that PCB design engineers need to master.
Measurement of Ripple in Switching Power Supply
To effectively reduce the output ripple of switching power supplies, we first need a reliable testing method. False waveforms caused by problems with the testing method cannot be rectified properly
Basic requirements: Use oscilloscope AC coupling, 20MHz bandwidth limit, unplug the probe's ground wire
1. AC coupling is the process of removing the superimposed DC voltage to obtain an accurate waveform.
2. Opening the 20MHz bandwidth limit is to prevent interference from high-frequency noise and to prevent erroneous results from being detected. Due to the large amplitude of high-frequency components, they should be removed during measurement.
3. Remove the grounding clip of the oscilloscope probe and use a grounding ring for measurement to reduce interference. Many departments do not have grounding rings, and if the error allows, they can directly measure with the grounding clamp of the probe. But this factor should be considered when judging whether it is qualified.
Another point is to use a 50 Ω terminal. According to the information on the Yokogawa oscilloscope, the 50 Ω module removes the DC component and accurately measures the AC component. However, few oscilloscopes are equipped with such specialized probes. In most cases, standard probes ranging from 100K Ω to 10M Ω are used for measurement, and the impact is currently unclear.
The above are the basic precautions when measuring switch ripple. If the oscilloscope probe does not directly contact the output point, it should be measured using twisted pair cables or 50 Ω coaxial cables.
When measuring high-frequency noise, the full passband of an oscilloscope is generally in the range of several hundred megahertz to GHz. Others are the same as above.
Different companies may have different testing methods. Ultimately, the first step is to have a clear understanding of one's own testing results, and the second step is to gain customer recognition.
