How to Measure Ripple in Switching Power Supplies
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.
About Oscilloscope
Some digital oscilloscopes cannot accurately measure ripple due to interference and storage depth. At this point, the oscilloscope should be replaced. Sometimes, although the bandwidth of old analog oscilloscopes is only a few tens of megabytes, their performance is better than that of digital oscilloscopes.
Suppression of Ripple in Switching Power Supply
For switch ripple, both theoretically and practically, there exists a D. There are usually five ways to suppress or reduce it:
1. Increase inductance and output capacitance filtering
According to the formula of switching power supply, the fluctuation of current in the inductor is inversely proportional to the inductance value, and the output ripple is inversely proportional to the output capacitance value. So increasing the inductance and output capacitance values can reduce ripple.
