Author:
Ally Winning, European Editor, PSD
Date
01/07/2026
PDF
Frederick Dostal, Subject Matter Expert for Power Management, Analog Devices
Bode plots are a useful tool to test power supplies. They provide accurate results for the stability of the loop, the phase margin of the loop, impedance, and a zero dB crossover figure, which indicates the speed of the loop, allowing easy comparisons from one power supply to the next. In a TechTalk last July, Frederik Dostal, Subject Matter Expert for Power Management at Analog Devices, described how the company has developed a simple and cost-effective way of generating bode plots using hardware that included the company’s LTpowerAnalyzer, ADALM2000 pocket oscilloscope and a PC. Analog Devices has now introduced an add-on board that extends the functionality of the set-up to simplify power supply design.
Dostal explained, “in the past, if you wanted to develop a power supply. You’d do calculations, then simulate it, then build hardware, and then test the hardware using equipment such as the LTpowerAnalyzer to generate a bode plot that will provide information on the stability and the speed of the power supply. But, what if you wanted to make changes to the stability of the power supply? That required a soldering iron to manually change the passives, and then the testing needs performed again. Sometimes there are parasitic effects, and that affects the results. So, it often can take several iterations before a the correct result is reached.”
The new compensation probe board for the LTpowerAnalyzer is designed to augment the test set-up, and provide the designer with the ability to experiment with the resistors and capacitors in the feedback loop. The EVAL-LTPA-COMPRB can function as either a programmable resistor, capacitor, or series resistor-capacitor network, depending on how it is connected to the DUT.
Dostal continues, “The compensation probe board is attached to the PC using USB to allow it to communicate with the software. On the other side, the board is attached to the compensation pin of the power supply. That allows different compensation components to be set easily through the GUI. Then, transient tests can be loaded using the different compensation components set by the software. The add-on board provides a way to modify the stability loop of any kind of power supply without needing to solder after every change of component.”
In the past, Analog Devices has offered a board with a resistor chain and different capacitors in parallel controlled by microswitches for the same purpose. Software control eases the process considerably compared to remembering the value of the components controlled by each DIP switch, and ensuring that they are properly set. Now, the designer only has to type in the resistor and capacitive values, where the DIP switch method required manual calculation. The compensation probe board only costs $90 and is now widely available. It can be used with the LTpowerAnalyzer, or independently however the user wishes. The resistance range covered is from 511Ω up to 100kΩ and the capacitance range offered by the board ranges from 5pF to 39nF.
