Et system LAB-SMS/E Series, Manual

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32 ET System electronic GmbH
ET-System Rippel Measurment Specification
Theoretical Analysis
The component of the output ripple is built by the output current and the equivalent series resistor of the output
capacitor. Picture 1 show a basic circuit which was used to simulate the ripple.
Picture 2 show the ripple without spikes. Picture 2 shows also the different between the used measurement band-
width. At this example the switching frequency of the converter was 80kHz (this is also the switching frequency of the
LAB/HP and LAB/SMS series).The red line shows the measured ripple by using a bandwidth of 20MHz and the blue line
shows the measured ripple by using a measure bandwidth of 300kHz.
This example shows that the measurement bandwidth have a strong influence of the measurement result.
The spike or noise of the ripple will generate by the switching noise of the power supply. The spikes which will be
measured strongly depend on the used measurement method. One point is the using measurement bandwidth the
other point is the test setup. The influence of the measurement method is show at picture 4. Picture 3 show the pre-
vious know circuit and also the same circuit with some added leakage component how are contribute to the output
noise.
This example show that the measurement bandwidth do influence the spikes or noise measurement.