Today, the demand for high-performance power systems is increasing, from applications in high-energy and efficient aerospace and automotive systems to applications in highly efficient battery systems with very low power consumption (such as consumer and medical electronics). Because of this demand in the market, it is particularly important to optimize the design of energy conversion to achieve the goal of high cost performance.

The center of all performance of the switching power supply system is the feedback control system. The feedback control system adjusts the energy conversion at all times to keep the output voltage of the power supply system constant to meet the power change required by the load.

In general, switching power supplies contain energy storage and current circuit devices, such as inductors, capacitors, diodes, transformers, and power switches (common low-loss MOSFETs). Most of these devices are in the control loop. In addition, the switching frequency of the power supply is very high, with extremely fast rise and fall time switching. Because of the relatively high switching frequency, the second-order effects of these devices may contribute to the overall performance of the power system.

Most circuit simulation kits are now able to demonstrate the overall performance of the switching power supply topology, and many engineers will consider the real power supply performance to be similar to the simulation model, but unfortunately many real circuits are far from the performance of the simulation circuit model, although the stability is the same as the simulation results. This is because the design of the printed circuit board, the aging of the device, and the parasitic effects are usually not reflected in the simulation model. In addition, the diversity of the load, the input voltage and the ambient temperature may cause the switching power supply to be unstable.

Improvements in the efficiency and performance of the switching power supply can be achieved by measuring and optimizing the open circuit frequency characteristic response of the control system.

The network analyzer can well measure the open-circuit transfer function. The network analyzer is a narrow-band frequency domain detection method, which can add sweep frequency excitation to the tested piece, and the test result is synchronized with the frequency of the added excitation. This tuning method enables the network analyzer to test very small signals, even noise included in the signals. In the face of high-frequency noise, large signal and electromagnetic interference in the switching power supply, the test is advantageous.

In the switching power supply control loop, the sweep excitation signal is injected mainly through the isolation transformer, and the input of the network analyzer is connected to each test point. Within the specified sweep frequency range, each frequency point gets a difference between the inputs, and the test results are presented in the form of Bode diagram. The Bode diagram gives the open-circuit frequency response characteristic curves of the two tested systems, the relationship between amplitude and frequency, and the relationship between phase and frequency. The stability parameters of the phase margin and gain margin can be easily obtained in the Bode diagram.