Noninvasive stability measurement of linear voltage regulator in the closed-loop condition

Abstract

Few factors may contribute to the stability of a linear voltage regulator (LVR). Among them is the value of the capacitor connected to the output terminal of the LVR, with the primary factor being the parasitic element of the capacitor, namely, equivalent series resistance. The LVR operation is based on the closed-loop system mechanism. LVR stability can be analyzed through two types of responses, namely, transient and frequency. This research focuses on the frequency response of the closed-loop system in terms of the phase margin at the unity gain frequency. Frequency response generates a more accurate outcome than transient response. The transient response can be acquired while the system is in the closed-loop condition, whereas frequency response can only be obtained in the open-loop condition. In this study, a noninvasive method is applied to obtain the LVR frequency response while the system is in the closed-loop condition. LTSpice software is utilized to simulate the LVR circuit. The simulation result is used as a reference for the actual hardware circuitry tests. The obtained outcome shows that the phase margin from the circuit simulation is similar to that of the hardware circuitry. Therefore, the noninvasive stability measurement method is valid for analyzing LVR stability by measuring the phase margin even in the closed-loop condition.