Stability Analysis of Power Supplies with the Bode 100

Focus:

In just under 6 minutes, this video offers a whiteboard explanation of the signal injection method of stability analysis (in other words, how to measure gain and phase margin of a power supply control loop). Following the explanation, the presenter demonstrates these same measurements using his company’s Bode 100 vector network analyzer and B-WIT 100 injection transformer . The device under test in this case is the LM317 linear regulator, but the same tests can be performed on switching regulators, or any power supply where you have access to (and can break) the feedback loop to insert a small injection resistor. Despite the brevity of the video, the concepts and test methods are clearly explained and within the demo, the presenter explains how to adjust your injection signal levels to be sure you’re not overdriving the control loop. He also explains a feature of the Bode 100, a shaped-level function which adjusts the VNA’s output signal level as a function of frequency to reduce the noise in the measurement.

What you’ll learn:

• How to measure the gain and phase margin of a power supply using the conventional signal injection method
• How to verify power supply stability

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Author & Publication:

Bernhard Baumgartner, Omicron Lab, YouTube, Sep 01 2011

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