The Measurement of Ripple in Switching Power Supplies
1. AC coupling is the process of removing the superimposed DC voltage to obtain the correct waveform.
2. Opening the 20MHz bandwidth limit is to prevent interference from high-frequency noise and to prevent measurement errors. Due to the large amplitude of high-frequency components, they should be removed during measurement.
3. Unplug the grounding clip of the oscilloscope probe and measure with a grounding ring to reduce interference. Many parts do not have grounding rings, and if the error is acceptable, they can be directly measured using the probe's grounding clamp. But this factor should be considered when determining 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 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, it is important to have a clear understanding of one's test results. **To gain customer recognition.
