Ripple test

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Through experimental comparison, we can find some issues that need to be paid attention to when using an oscilloscope probe to test the output ripple of a power supply. A more accurate way to test the ripple is to take off the cap of the probe, connect a 0.1uf ceramic capacitor or a 0.1uf ceramic capacitor plus a 1uf electrolytic capacitor between the probe and the outer ring ground, and then perform a ripple test. This is the most accurate way. Because the oscilloscope probe is also equivalent to an antenna under normal circumstances, it can receive some external interference noise. Affect the actual test effect. It is necessary to add a bypass capacitor at the outermost end to filter out the high-frequency interference noise. 1. Use the most primitive method Use the most primitive method, clamp the oscilloscope probe directly on the output line of the power, and observe the ripple waveform on the oscilloscope.

From the tested waveform, we can see that there is an interference waveform with a peak value of about 74mV and a frequency of 85KHz. 2. Remove the cap of the oscilloscope probe Remove the cap of the oscilloscope probe, directly connect the probe to the output DC line, and observe the waveform of the oscilloscope.

From the tested waveform, we can see that there is an interference waveform with a peak value of about 74mV and a frequency of 85KHz.

3. Test the capacitor in parallel on the probe Connect a 0.1uf ceramic capacitor on the probe of the oscilloscope probe and the outer ground ring next to it, and then test the ripple.

From the tested waveform, we can see that the average ripple is around 17mV, and there is no spike interference waveform.

4. Test without ground clip Remove the conventional ground clip wire of the oscilloscope probe, and use a short wire to directly solder the ground ring and the output negative pole of the probe, and then test the ripple.

From the waveforms tested, there is no obvious difference with the third test method above. The average ripple is around 17mV, and there is no spike interference waveform.

5. Test the capacitor in parallel on the power segment Put the cap of the probe on and connect 0.1uf ceramic capacitor, use a clip to clamp the output end directly to test the output ripple.

From the tested waveform, we can see that there is a spike interference waveform, the peak ripple is about 63mV, but it is about 10mV smaller than that without adding capacitor.

6. Standard ripple test method