Frequency Response Analysis

Video Sample: PSM1700 PsimetriQ
Application: Testing loop stability

Introduction

This video sample illustrates various display options available to a user of the PSM1700 when in Frequency Response Analysis mode. In this example, the PSM1700 is testing the closed loop stability of a switched mode power supply when connected to the control loop of the supply via an injection resistor and an N4L injection transformer.

This one minute video clip is not edited and represents real measurements over a one minute period with the following sequence of font panel and device under test changes.

What happens in the video?

1. In FRA mode, the gain / phase margin option is selected.
2. The power supply is switched on with a 5% load applied and the 'Start' sweep button on the PSM1700 is pressed. A frequency sweep from 50Hz to 30kHz runs and after the sweep, gain and phase margins are automatically presented.
3. The 'Table' button is pressed and a table of 'Frequency', 'Gain' and 'Phase' values for the last 20 test frequencies is shown.
4. The '' button is pressed and the table scrolls up by 15 lines.
5. The '' button is pressed and the table scrolls up by 15 lines to the first 20 test frequencies.
6. The 'Graph' button is pressed and the display returns to the bode-plot graph.
7. The '' key is pressed a number of times taking a cursor to the gain crossover frequency (gain = 0dB) which is 273Hz.
8. The 'Real Time' button is pressed showing real time results of 'Gain', 'Phase', 'CH1 Magnitude' and 'Frequency' at the selected cursor point. Notice that the Gain is 0.0x dB.
9. The load on the output of the PSU is changed from 5% to 50% and at that point, the Gain reading increases to +18 dB.
10. The 'Start' sweep button is pressed and a new sweep is executed with the new 50% load results overwriting the original 5% sweep results and at the end of the sweep, the new gain / phase margin values are presented.

Next steps

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