Switching Power Supply Control Loop Stability Verification
Frequency response characteristics of a switching power supply loop, if the load characteristics of the power supply have a gain equal to 1 (0dB) at a certain frequency and a phase shift of 180°, then the power supply control loop
will have enough energy to return to the system and maintain the oscillation at this frequency due to the presence of in-phase positive feedback (this phase shift plus the original setting of 180° phase shift, for a total phase shift of 360°).
Oscillation. To avoid similar destructive instability in the power supply system, feedback compensation components are normally used in the loop control circuit to reduce the high-frequency
to reduce the gain at the high-frequency end so that the switching power supply remains stable over the preset frequency range.
Signal resistor (Inserted Resistor) into the loop control circuit of the power supply, inject a specific amplitude and frequency range of the swept interference signal (OUT), when the interference signal reaches a certain amplitude, the loop system will respond to the interference signal, and then use a frequency response analyser on the power supply loop output (CH2) and the power supply loop interference signal injection (CH1) ratio tracking at the same time. ) at the same time for ratio tracking measurements, then you can derive the frequency and gain and phase of the relationship between the curve - Bode Plot Graph (Bode Plot Graph).
In the actual test process should pay attention to the link is the location of the injection resistor, as well as the size of the resistance value. In order to reduce the measurement error, the actual test is generally selected 10 ~ 100Ω resistance; the size of the interference signal is generally required to its amplitude can not exceed 5% of the output voltage, otherwise the measured results are inaccurate.
