[introduction] the core index that ripple is power source, the ripple noise that how reduces power supply is the problem that most user cares, it is from power source design, exterior circuit does plan to improve on one hand, should have on the other hand more accurate the more appropriate method that checks ripple noise.
The ripple of power source and noise introduce
Ripple and noise namely: The is the same as frequency with mains switch frequency wave motion of the overlay on output of direct current source is ripple, high frequency cacophony is noise. Specific like the graph 1 is shown, frequency is inferior and the wave motion that has the law is ripple, aiguille part is noise.
Graph noise of ripple of 1 power source
Non-standard ripple checks
The power source signal of a 3.3V is received in oscillograph, probe archives use X10 archives, undertake the measurement of power source ripple, click [Auto Setup] later, the course mediates horizontal time base, perpendicular archives with perpendicular deflection, can get 2 are shown as follows pursueing.
Graph 2 non-standard ripple check
Can see from inside the graph, measures weaveform places a lot of miscellaneous noise and clutter, lump of weaveform of dc, communication, do not have the observation ripple of method clarity, bring about cannot accurate measurement the value of ripple. A lot of engineers measure ripple to appear because did not use normative ripple measurement technique,this kind of circumstance is.
Normative ripple checks a method
1. Probe should choose appropriate archives, if voltage is bigger, perhaps ask to X10 file can be used below higher case to bandwidth, the proposal below general case uses X1 file, avoid needless noise attenuation to affect the measurement of ripple.
Graph 3 probe archives choice
2. Ripple is belonged to is communication composition, so ” passageway coupling ” means can be used ” communication ” means, restrict the input of dc signal, if pursue,4 are shown.
3. But proper use ” bandwidth is restricted ” function, optional choose ” 20MHz ” bandwidth limitation, filter of will needless high frequency noise is divided, if pursue,4 are shown.
Graph setting of parameter of 4 passageways interface
4. Because check the meeting in the environment to have a lot of EMI (electromagnetism is disturbed) , oscillograph is tall block equipment, signal of meeting general EMI introduces test result, cause measure a result to slant big. Correct measurement means should be to use ground connection bedspring to so that reduce what electromagnetism disturbs to introduce,have ground contact. Mix with ground connection bedspring with crocodilian clip ground connection contrast pursues as follows be shown:
Graph means of 5 ground connection is comparative
5. Spark means can choose edge to spark, spark mode chooses Auto/Normal all but.
6. Adjust horizontal time base appropriately, perpendicular archives with perpendicular deflection, make undee signal is in the center of screen show with better effect, specific following graphs show captured ripple 6 times.
Graph 6 ripple capture
Correct ripple measures means to be able to be caught clearly catch correct ripple, reduced the effect of unwanted noise and clutter to ripple, checking a result is a clean ripple, in such foundation ripple of aspirant travel power source is measured, can more accurate measurement the value of ripple, then more accurate appraise measures power source quality.
7. Measure an analysis. Ripple test expresses commonly with peak peak value, can use [Measure] undertake be metricaled automatically, ZDS series oscillograph supports the parameter of 51 kinds of real significances to measure statistical function, be based on the parameter that ripple measures on the foundation of complete memory deepness, also perhaps can use ” one key cursor ” undertake the hand is moved measure, following graphs are shown 7 times.
Graph 7 results analysis
Can see from inside measure, the peak peak value of ripple of this second power source is 18mv, intel sets in ATX12V standard, + peak value of peak of 12V output ripple must not exceed 120mv, + 3.3V and + peak value of 5V ripple peak must not exceed 50mv, quality of smaller power source jumps over ripple tall.
3 paces finish ripple noise to test idea
ZDS5054A oscillograph has the power source with perfect function to analyse a function, OK and special measure power source to output ripple, noise conveniently.
The first pace: The archives with right choice after probe, click [Auto Setup] one key captures undee signal;
The 2nd pace: Click [passageway 1] enter passageway interface, instead of passageway coupling means [communicate] ;
The 3rd pace: Open power source to analyse a function, choose [output ripple] , test type can choose ” ripple ” and ” noise ” two kinds, end the basis that frequency filter gets ripple except high frequency composition, following graphs 8 meetings check a ripple automatically to measure an outcome.
Graph 8 Ripple checks a function automatically
Note: There are 4 projects in measuring result form:
Ripple / noise voltage: The voltage virtual value after filter wave;
The greatest peak value: The voltage after filter wave is the biggest peak value;
The least peak value: The tension after filter wave is the least peak value;
Frequency: The frequency of the signal after filter wave.
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