Test Power Supply with Different Compensation

Power Tip Test Power Supply with Different Compensation

2026-05-04 From Frederik Dostal* | Translated by AI 2 min Reading Time

Power supplies should generate a fixed output voltage. Compensation components are used to optimize the control loop of a voltage converter. This power tip shows how different compensation settings can be tried out in a very short time.

Figure 1: Switched-mode voltage transformer with corresponding compensation components for adjusting the control loop speed and stability.(Image: ADI) — Figure 1: Switched-mode voltage transformer with corresponding compensation components for adjusting the control loop speed and stability.
(Image: ADI)

The output voltage of a power supply must not oscillate and should remain constant in the event of load transients and changes in the input voltage. In order to optimize the control loop of a clocked voltage converter, many power supply ICs have compensation pins.

These can be wired with appropriate compensation components - capacitors and resistors - in such a way that the highest control bandwidth is achieved while ensuring control loop stability. A control loop must be set because the compensation must be implemented differently depending on the operating conditions and the selection of external components in the power path.

Figure 1 shows a buck regulator with the corresponding compensation pin V_c.

Choice of Compensation Components

The compensation components can be selected using appropriate calculation and simulation programs such as LTpowerCAD and LTspice. However, the parasitic effects of the PCB layout also play a certain role. A power supply should therefore always be checked in hardware. This is where the selection of the compensation components is finally checked and confirmed.

This step is time-consuming when designing a power supply. A bode diagram or a load transient measurement must be carried out using the LTpowerAnalyzer, for example. If the result does not meet the design objectives, it must be optimized. This involves desoldering the compensation components and replacing them with other values. This is a laborious and time-consuming process.

Figure 2: The EVAL board LTPA-COMPRB with which different settings can be made on the compensation pin in a very short time via a graphical user interface.(Image: ADI) — Figure 2: The EVAL board LTPA-COMPRB with which different settings can be made on the compensation pin in a very short time via a graphical user interface.
(Image: ADI)

Figure 2 shows a board available from Analog Devices, which is called a 'compensation probe'. This board can be connected with the solder contacts on the right-hand side to the compensation pin and to the ground pin of any power supply.

The circuit board therefore replaces the compensation components in the red rectangle in Fig. 1. The circuit board is connected to a PC on the left-hand side using a USB cable.

Test the Values of the Compensation Components

After connecting the hardware, the free LTpowerAnalyzer software is started. In a graphical user interface, it quickly switches between different values of the compensation components. In combination with the LTpowerAnalyzer, it is then possible to create bode diagrams and carry out load transient tests with different compensation settings.

Figure 3: Selection of compensation components via a graphical user interface.(Image: ADI) — Figure 3: Selection of compensation components via a graphical user interface.
(Image: ADI)

Figure 3 shows the software interface of the EVAL board LTPA-COMPRB (Compensation Probe). Here, settings of resistance values between 511 Ω and 100 kΩ and capacitor values between 5 pF and 39 nF can be selected. The internal series resistance of the capacitor is also displayed and taken into account. If this compensation board is connected to the ground connection of the voltage converter IC to be tested and to the compensation pin using only short connecting cables, various compensation component values can be selected precisely, easily and quickly.

Checking and optimizing the control loop stability of a power supply is not only easy but also very efficient with a "compensation probe" such as the EVAL-LTPA-COMPRB. Different compensation settings can be tried out in a very short time. This not only creates better voltage supplies, but also enables the design to be completed in less time. (kr)

Frederik Dostal is Field Application Engineer for Power Management at Analog Devices in Munich.

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Power Tip Test Power Supply with Different Compensation

Choice of Compensation Components

Test the Values of the Compensation Components

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