Power supply ripple refers to the periodic AC component appearing at the output of a DC power supply. Its amplitude is usually represented as peak-to-peak or peak-to-valley, as shown in Figure 1. Power supply ripple is mainly caused by waveform imperfections during power conversion, such as voltage changes caused by the switching transistors turning on and off during the operation of a switching power supply. Power supply ripple can affect the normal operation of equipment, especially for precision electronic equipment and analog circuits that require stable power supplies.
Figure 1. Power supply ripple and noise
Suppressing and reducing power supply ripple to a reasonable range is one of the main goals in power supply circuit design. Therefore, mastering the correct power supply ripple testing methods is crucial for subsequent power supply debugging and ripple design optimization. An oscilloscope is typically used to measure power supply ripple. By setting appropriate trigger conditions and measurement ranges, the waveform and amplitude of the ripple are observed and recorded. Furthermore, other instruments and equipment, such as a ripple coefficient tester, can be used to further analyze and quantify the characteristics of the ripple.
To ensure the observation of a true and reliable ripple waveform, the following points should be noted when measuring output voltage ripple using an oscilloscope. The correct method is shown in Figure 2.
Figure 2
1. Select AC coupling mode on the oscilloscope;
2. To ensure signal-to-noise ratio, select X1 for probe attenuation during power supply ripple testing;
3. Set the bandwidth limit to 20MHz to avoid high-frequency noise affecting ripple measurement;
4. Minimize ground loops; a spring grounding ring is recommended as shown on the right side of Figure 2;
5. Place the probe close to both sides of the capacitor;
6. Avoid simultaneously testing waveforms at other points using other oscilloscope channels.
Using the correct measurement methods described above will allow you to observe a ripple waveform similar to the one shown below.
Figure 3 Ripple waveform
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