Introduction of Average Current Mode Control of Switching Power Supplies

For all power supply technology the controller design for SMPS has always been a complicated problem as well as also a unique topology that could be optimum is developed. For designing the control unit for the power converters there are two basics approaches that are explained below;

1.      Voltage-mode control scheme

2.      Current-mode control Scheme

For the PWM dc-dc power converters previously it was believed that the current mode control technique is the best approach to design until the introduction of voltage mode controller through the IC Unitrode Corporation. It becomes clear after the introduction of this controller that there is no specific scheme that could provide the exact result for all power supply applications. Moreover, to design the control circuits for SMPS the current-mode technique is still a large approach that is frequently used.

We further explain the detail of these two approaches in detail. Mostly in power converters the current mode control architecture is largely used because of its current limiting along with current-sharing capabilities (Dixon L. H., 1990) (Gallaher, 1967). Recently, to improve light load efficiency constant on-time current mode control has been generally used, to save switching related loss because it help in reducing the switching frequency (Maxim;, 2003) (STMicroelectronics, PM6685 datasheet., 2007).

By the researchers another method is studied named as digital control methods of PWM dc-dc converters has been accepted. Because of their ability of lower sensitivity in the system noise along with the variation of analog component, with other digital system it is easily integrate, and it have ability to implement the complicated control techniques, and by software it is possible to update controller (Peterchev & Sanders, 2006) (Saggini, Stefanutti, Tedeschi, & Mattavelli, 2007). Digital current-mode control technique is the major method that is depends on the feedback of the inductor current to perform controlling with the help of current sensor. The main objective of the controller is to maintain both the current like current of the inductor and the reference current, consequently fast transient response is acquire as well as overload protection built-in. The following problems have to be considered to perform a practical digital current control mode; first issue which we discussed is that to develop a low noise, wide bandwidth, simple as well as lossless current sensing techniques. An algorithm is the second issues that are insensitive to computational time delay. Due to requiring a precise conversion circuit there is the still issue in first problem. By performing some predictive algorithms the second issue might be handled and calculate the switching cycle duty ratio. The aim of this paper is to introduce an Average Current Mode Control of Switching Power Supplies for dc-dc converters. An appropriate duty cycle is calculated and it predicts that regulate the valley current.

Block diagram ACMC is proposed as the below diagram; the phase modulated series resonant converter used the power converter that is synchronized by the switching of converter through the load pluses that enables the converter switches for the half load by the switching frequency.