Feedback Injection for Low-Cost Dynamic Testing of DC–DC Power Supplies

Dynamic characterization of DC–DC power supplies typically requires dedicated dynamic voltage sources and electronic loads, which are often expensive and not readily available in low-cost laboratory environments. This creates a need for simple and flexible solutions capable of performing reliable line and load transient tests without complex auxiliary hardware. This paper presents a cost-effective technique for the dynamic testing of DC–DC power supplies, which can be applied with high versatility to both line and load transient testing. It is shown that injecting a perturbation signal into the feedback loop of a standard DC–DC regulator enables the regulator to operate either as a dynamic voltage source or as a dynamic electronic load, thus supporting both transient and small-signal AC characterization of a power supply under test. Analytical guidelines are provided to determine the static operating conditions and the achievable bandwidth of regulators operating in Dynamic Source Mode (DSM) and Dynamic Load Mode (DLM). The impact of voltage-mode and current-mode control strategies, as well as different error amplifier implementations, is investigated. Experimental line and load transient tests are carried out on interconnected switching and linear power supplies using Texas Instruments PMLK Series BUCK, BOOST, and LDO boards operating from 3.6 W to 36 W, with crossover frequencies up to 20 kHz. Measured injection gains and transient responses confirm the analytical predictions and demonstrate that FIT provides a simple, reliable, and cost-effective solution for dynamic testing of low-power DC–DC converters.