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如何测试输出纹波和噪声电源

更新时间：2019-12-19 16:20:04 大小：32K 上传用户：yuyw99查看TA发布的资源 标签：电源 下载积分：2分 评价赚积分 （如何评价?） 打赏 收藏 评论(0) 举报

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The switching power supplies (either step-down
regulators, or isolated DC-DC converters, or OFFLINE power supplies) have the fundamental advantage of high efficiency i.e. low power dissipation
when compared to linear voltage regulation.
However the switching technique, that is beneficial
to raise the efficiency, has an associated weakness
i.e. the output voltage has always an AC content.
The typical output ripple and noise of a switching
power supply is as shown in fig. 1

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HOW_TO_TEST_OUTPUT_RIPPLE_AND_NOISE.pdf 32K

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APPLICATION NOTE  
HOW TO TEST OUTPUT RIPPLE AND NOISE OF  
POWER SUPPLIES  
The switching power supplies (either step-down  
However the switching technique, that is beneficial  
to raise the efficiency, has an associated weakness  
i.e. the output voltage has always an AC content.  
The typical output ripple and noise of a switching  
power supply is as shown in fig. 1.  
regulators, or isolated DC-DC converters, or OFF-  
LINE power supplies) have the fundamental advan-  
tage of high efficiency i.e. low power dissipation  
when compared to linear voltage regulation.  
Figure 1. Output ripple and noise of a switching power supply  
Four AC components can be identified:  
The above mentioned parameters are normally  
specified by the peak to peak amplitude so that the  
best method for testing is by an oscilloscope with a  
bandwidth of 20 MHz.  
-
low frequency ripple at 2f being f the AC mains  
frequency  
-
high frequency ripple due to Pulse Width Modu-  
lation (PWM) to obtain the required line and load  
regulation.  
Care must be taken when using the scope probe.  
Fig. 2 shows a wrong method because the ground  
wire of the probe can collect radiated noise and the  
scope display is strongly dependent on the probe  
position.  
-
-
the switching noise that has the same frequency  
of the switching PWM  
the aperiodic random noise that is not related to  
the AC source frequency and/or the switching  
frequency.  
Fig. 3showsa bettermethodbecausethecollection  
of the radiated noise is minimized.  
AN647/0594  
1/3  
How to test the output ripple and noise of power supplies  
Figure 2. Wrong output ripple and noise test  
+
Power supply  
GND  
Figure 3. Correct output ripple and noise test  
+
GND  
Power supply  
The ground ring of the probe is pressed directly  
against the output ground of the power supply and  
the tip is in contact with the output voltage pin.  
A preferred method is shown in fig. 4: the waveform  
displayed on the scope must be multiplied by a  
factor 2.  
Figure 4. Preferred method to test output noise and ripple  
220nF  
Coax cable  
50 Ohm  
+
to AC input  
of scope  
Power supply  
50 Ohm  
GND  
2/3  

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