With the 20M oscilloscope bandwidth as the limit standard, the voltage is set to PK-PK (effective value is also measured), and the clip and ground wire on the oscilloscope control head are removed (because the clip and the ground wire will form a loop, like an antenna receiving Noise, introduce some unnecessary noise), use a grounding ring (it is also possible not to use a grounding ring, but the error generated by it should be considered), connect a 10UF electrolytic capacitor and a 0.1UF ceramic capacitor in parallel on the probe, and use an oscilloscope The probe of the oscilloscope should be tested directly; if the oscilloscope probe is not directly in contact with the output point, twisted pair or 50Ω coaxial cable should be used for measurement.

The output ripple of switching power supply mainly comes from five aspects: input low-frequency ripple; high-frequency ripple; common-mode ripple noise caused by parasitic parameters; ultra-high-frequency resonance noise generated during switching of power devices; ripple noise.

1. Channel settings:

Probe: First choose the voltage probe method. Then select the attenuation ratio of the probe. It must be consistent with the attenuation ratio of the probe actually used, so that the number read from the oscilloscope is the real data. For example, if the voltage probe used is set to ×10, then at this time, the option of the probe here must also be set to ×10.

2. Trigger settings:

Source: the channel actually selected, for example, CH1 channel is going to be used for testing, then CH1 should be selected here.

Trigger mode: If you are observing the ripple signal in real time, select 'Auto' to trigger. The oscilloscope will automatically follow the changes of the actual measured signal and display it. At this time, you can also display the measured value you need in real time by setting the measurement button. However, if you want to capture the signal waveform during a certain measurement, you need to set the trigger mode to 'normal' trigger. At this point, it is also necessary to set the size of the trigger level. Generally when you know the peak value of the signal you are measuring, set the trigger level to 1/3 of the peak value of the signal you are measuring. If not known, the trigger level can be set slightly lower.

3. Sampling length (second/grid):

The setting of the sampling length determines whether the required data can be sampled. When the set sampling length is too large, the high-frequency components in the actual signal will be missed; when the set sampling length is too small, only part of the measured actual signal can be seen, and the real actual signal cannot be obtained. Therefore, in the actual measurement, it is necessary to rotate the button back and forth and observe carefully until the displayed waveform is a real and complete waveform.

4. Sampling method:

It can be set according to actual needs. For example, if it is required to measure the P-P value of the ripple, it is best to choose the peak measurement method. The number of sampling times can also be set according to actual needs, which is related to the sampling frequency and sampling length.

5. Measurement: