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Summary
Every power supply has a unique control loop which can change significantly with line, load, tsubperature, and component variations. It is important to measure the loop and ensure that the gain and phase margins are properly designed for a rugged power supply. The entire loop gain must be studied, not just the crossover region, to ensure that the system will always be stable.
Unusual loop gains are relatively common in power supply design, resulting in conditionally stable systems, and loops with multiple crossings. Using the AP300 analyzer will quickly and cleanly measure all such loops.
References
- “Frequency Response of Switching Power Supplies, Parts 1-5”, Power systems Design Magazine, Design Tips Archive. http://www.powersystemsdesign.com
- “AP Instruments AP300 User Manual”, http://www.apinstruments.com/files/Model300.pdf