What are the five main sources of ripple in the output of a switching power supply?
1. Channel settings:
Coupling: that is, the choice of channel coupling method. Ripple is an AC signal superimposed on a DC signal, so if we want to test the ripple signal we can remove the DC signal and just measure the superimposed AC signal directly.
Wideband limit: Off
Probe: first choose the way of voltage probe. Then choose the attenuation ratio of the probe. Must be consistent with the actual attenuation ratio of the probe used, so that the number read from the oscilloscope is the real data. For example, the voltage probe used is placed in the ×10 gear, then at this time, the options for the probe here must also be set to ×10 gear.
2. Trigger settings:
Type: Edge
Source: the actual channel selected, such as, ready to use the CH1 channel for testing, then here should be selected as CH1.
Slope: rising.
Trigger Mode: If the ripple signal is being observed in real time, select 'Auto' trigger. The oscilloscope will automatically follow the actual measured signal and display it. At this time, you can also set the Measurement button to display the value of your desired measurement in real time. However, if you want to capture the signal waveform during a particular measurement, you need to set the trigger method to 'Normal' trigger. In this case, you also need to set the magnitude of the trigger level. Generally when you know the peak value of the signal you are measuring, set the trigger level at 1/3 of the peak value of the measured signal. If you don't know, the trigger level can be set slightly smaller.
Coupling: DC or AC..., generally use AC coupling.
3. Sampling length (sec/g):
The setting of the sampling length determines whether the required data can be sampled. When the set sampling length is too large, it will miss the high-frequency components of the actual signal; when the set sampling length is too small, you can only see the actual signal measured locally, the same can not get the real actual signal. Therefore, in the actual measurement, you need to rotate the button back and forth, carefully observe until the displayed waveform is a real complete waveform.
4. Sampling mode:
Can be set according to the actual need. For example, if you want to measure the P-P value of the ripple, it is better to choose the peak measurement method. Sampling times can also be set according to actual needs, which is related to the sampling frequency and sampling length.
5. Measurement:
By selecting the peak measurement of the corresponding channel, the oscilloscope can help you display the required data in time. You can also select the frequency, maximum value and root mean square value of the corresponding channel.
Through reasonable settings and standardised operation of the oscilloscope, you can surely get the required ripple signal. However, during the measurement process, care must be taken to prevent other signals from interfering with the oscilloscope probe itself, so as to avoid the measured signals from being untrue.
Measurement of ripple value through the current signal measurement method refers to the measurement of AC ripple current signal superimposed on the DC current signal. For constant current sources with high ripple index requirements, i.e. constant current sources with small ripple requirements, the direct current signal measurement method can obtain a more realistic ripple signal. Unlike the voltage measurement method, the current probe is also used here. For example, continue to use the oscilloscope described above, plus a current amplifier and a current probe. At this point, just use the current probe to clamp the current signal output to the load, you can carry out the current measurement method to measure the ripple signal of the output current. As with the voltage measurement method, the setup of the oscilloscope and current amplifier is the key to sampling the true signal throughout the test.
