Average Current Controller for Buck Converter with Reduced Comparator Delay
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Solution Overview
Problem
Conventional average current controllers face challenges in maintaining consistent average current levels due to delays from signal processing and difficulty in controlling current when on-time is short, especially in buck converters used for LED driving circuits.
Innovation Solution
An average current controller comprising a first comparator, multivibrator, timing generator, integrator circuit, second comparator, up/down counter, and digital/analog converter, which generates a TAVG pulse signal and charges/discharges a capacitor to determine the average switching period and voltage state, allowing for precise control of the main switch current and reducing the impact of comparator delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional average current controller uses two comparators to sense average current and peak current, then current control is achieved, but signal processing delay causes average current level to change
Solution Approach 1:
The patent extracts the peak current sensing function from the traditional two-comparator architecture and implements it through capacitor voltage comparison. By using a single comparator to compare capacitor voltage (which represents peak current information) with a reference voltage, the design eliminates the signal processing delay inherent in dual-comparator systems while maintaining both average and peak current control capabilities.
Solution Approach 2:
The capacitor serves as an intermediary element that stores peak current information as voltage. Instead of directly comparing two current signals with two comparators, the system uses the capacitor to mediate the information transfer, allowing a single comparator to perform both average and peak current sensing functions without timing delays.
2Productivity
If on-time is very short in buck converter operation, then switching frequency increases, but current control becomes difficult
Solution Approach 1:
The patent replaces traditional current sensing and control mechanisms with a voltage-based control system. By converting current information into voltage signals through resistors and capacitors, and using voltage comparators instead of current comparators, the system achieves accurate current control even at high switching frequencies where traditional current-mode control becomes difficult.
Solution Approach 2:
The system changes the control parameter from direct current comparison to voltage comparison. By transforming the control domain from current-mode to voltage-mode, the controller can accurately regulate current even when on-time is very short and switching frequency is high, as voltage signals can be processed more quickly and accurately than current signals.
3Stability of the object's composition
If off-time control method is used to maintain constant off-time, then off-time is controlled constantly, but average current changes due to varying ripple current
Solution Approach 1:
The patent implements a feedback mechanism where the capacitor voltage (representing peak current) is continuously compared with a reference voltage. Based on this comparison, the controller adjusts the on-time to maintain the desired average current level, even when off-time is constant and ripple current varies. This closed-loop feedback ensures accurate average current control independent of ripple variations.
Data Source
AI summary
The present invention relates to an average current controller, an average current control method and a buck converter using the average current controller. The average current controller includes a first comparator for generating a high H signal, a multivibrator for generating a TAVG pulse signal by receiving a high H signal outputted from the first comparator, a timing generator for generating a signal CH_ON to charge/discharge a capacitor by using at least the TAVG pulse signal, an integrator circuit unit for charging/discharging the capacitor, a second comparator for outputting a corresponding signal, an up/down counter for increasing or decreasing a counting value and a digital/analog converter for outputting by converting an output (digital signal) of the up/down counter into an analog signal.