Consideration for the Overcurrent Limiting Control Circuit of the DC-DC Converter

摘要

In the controller of the dc-dc converter, the overcurrent limiting control circuit is often prepared to protect the power stage of the dc-dc converter and/or the load. In this case, the operation of the dc-dc converter is divided into to major modes, i. e., the constant voltage-regulated and overcurrent-limited modes. In the overcurrent-limited mode, the controller may be affected easily by the switching noise from the power stage because the gain of the overcurrent-limiting circuit is relatively high. The integral compensator is used usually to suppress the influence of this noise. However, when the gain is made larger, the converter in the overcurrent-limited mode easily becomes unstable. The purpose of this paper is to present the overcurrent-limiting control circuit composed of not only the integral compensator but also the derivative one to improve the dynamic characteristics in the overcurrent-limited mode. Also, the steady-state and dynamic characteristics in the overcurrentlimited mode of the converter are analyzed theoretically and experimentally. As a result, the circuit conditions in steady-state are defined for the foldback current-limiting, constant current, and voltage drooping characteristics. Moreover, it is revealed that the stability in the overcurrent-limited mode and the transient response with the step change of the load from the voltage-regulated mode to the current-limited one can be sufficiently improved by employing the relatively large overcurrent-limiting coefficient and the appropriate rate and reset time of the derivative and integral compensators.