Power supply ripple is power performance of the most intuitive performance, is the power supply output voltage fluctuations, if it is a switching power supply, the output ripple is regular swing, oscillation frequency is equal to the switching frequency, because the formation of the ripple current flows through the output capacitor on the ESR of capacitance caused by the pressure drop, switching power supply continuously has the pulse electric current flowing through the capacitor, so its frequency is equal to the switching frequency ripple, ripple superimposed noise of power supply system will be passed to the power of the chip pins, affect the performance of the chip,
I just do one piece of motion control board of power system test, intuitive to show you the testing process and methods of the power supply ripple, oneself also make a note at the same time, as shown in the figure below, M is my motion control board, P is for M power supply switch power supply, S is the USB oscilloscope OSC802 loto
The power of the motion control board M parts of schematic and PCB layout as shown in the figure below:
We need to test the V and G on both ends of the power supply ripple, to see if the power supply system has reached the requirement of design,
, of course, first of all, we know you want to use the oscilloscope to test the ripple size AC coupling gear, get rid of our dc component, you don't care about me for the convenience of use, for the first time longer oscilloscope probe ground wire, as shown in the figure below:
Power supply ripple is unlikely, because the ground is longer, the figure shown in yellow line circulation path in this area will be absorbed radiation interference, superimposed on the basis of real ripple, in this case, I test results are as follows:
Measured roughly 80 mv ripple, even the noise of the superposition of more than 100 mv (use OSC802 50 mv/div gear), fearing that the circulation path receiving noise impact, I improved the testing methods, minimize the loop area, will be to minimize interference, query, grounding spring is used to measure the loop area is very small, but you don't have ground spring, temporary with a paper clip to break off the straight, winding grounding a simple spring,
In this way, you can use a small loop area is measured between V and G ripple
Measurement results were improved a lot, ripple becomes very clean and tidy, probably about 20 mv had measured ripple, (use OSC802 20 mv/div gear) as shown in the figure below:
Seems to be still more clean power supply system of the ripple, and stable in about 20 mv, basically met us at the beginning of the design requirements, but also see, just changed the ground test length (actually change the loop area) test the result of the difference is so large, in order to be prudent, I have borrowed a desktop oscilloscope, the two operations repeated again, virtual oscilloscope and desktop digital oscilloscope got the same conclusion, respectively is 80 mv and ripple of 20 mv:
So to be sure, the measurement of the power supply ripple, is indeed a need to use the AC coupling, and then use spring to grounding to minimize the loop area can, if there is no ground spring can be conveniently made a completely, in addition, the USB power supply ripple as oscilloscope OSC802 measurement, 20 mv ripple can be easily measured and clear show that
I repeat again for the whole process video on youku, convenient people communicate with each other:
Video is as follows:
https://v.youku.com/v_show/id_XNDA0NDcxMTAxNg==.html? SPM=a2h0j. 11185381. Listitem_page1. 5 ~ A
QQ: 173393190.