Research on Stability Margin of Linear Current Source Using New Loop Compensator

  • He Liu

Abstract

The linear current source is realized by the op amp and the power switch. By controlling the driving level of the op amp output, the equivalent resistance of the switch is adjusted, so as to achieve the purpose of stabilizing the output current. It is widely used in automatic testing, measurement and other applications. Because the parasitic capacitance of the switch will affect the stability of op amp output, when the linear current source has a wide working range, the traditional type II compensator cannot meet the stability requirements that the phase angle margin is more than 60° and the gain margin is more than 10dB under all operating conditions, and the dynamic characteristics will be greatly affected. In this paper, the AC small signal model of linear current source loop is established, the transfer function is derived, and the variation trend of stability margin at different operating points is obtained. In order to realize the fast step of linear current source at different working points, and avoid the problems of slow response speed and high output current overshoot caused by insufficient phase angle margin in the dynamic process, a new compensator is adopted in the control loop, and the corresponding design criteria are proposed in this paper. Using the proposed method, the measured loop through frequencies of the linear current source at 0.3A and 0.5A are 24.8kHz and 38.9kHz respectively, and the phase margin is 131.7° and 130.5° respectively, and the gain margin is 18.6db and 17.4db respectively. The phase frequency characteristic curve is maintained at 60° within 500kHz. Above all, the dynamic response speed is fast, which verifies the correctness of the theoretical analysis.

Published
2021-06-17
How to Cite
He Liu. (2021). Research on Stability Margin of Linear Current Source Using New Loop Compensator. Design Engineering, 48 - 58. Retrieved from http://www.thedesignengineering.com/index.php/DE/article/view/2113
Section
Articles