原创 固定输出稳压器相位裕度的测量计算

      It is easy to measure regulators’ stability and control loop behavior with vector network analyzer (such like PSM1700 ), The first element required for this method is to breaking the control loop and then inject a disturbance signal. To achieve this, it is necessary to insert a small resistor (10Ω to 100Ω) into the loop at a suitable point where the small resistance has negligible effect .

       But many voltage regulators are of the fixed output variety and include the voltage divider internal to the regulator. for them aforementioned approach is not available.

      According to fundamenal of power electronics,  we determined the relationship between phase margin and group delay Tg as:

        Omicron Bode100, together with Picotest current injector TJA2111A, allows direct measurement of the output impedance, group delay and Q of the system. Using this information the phase margin of the system can be calculated without breaking the feedback loop of the controller. This method is called "non-invasive.”

       For example, Measure Low-dropout regulator L4949 in two cases: with and without 1 ohm resistor in series with buffer capacitor.

      We get the result that:

Phase Margin with 1 ohm resistor:      71°

Phase Margin without 1 ohm resistor: 5.2°