Buck Converter Dual Feedback Loop for Voltage Accuracy
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Solution Overview
Problem
Conventional buck switching regulators suffer from voltage offset due to output ripple, which reduces the accuracy of the output voltage and lacks fast transient response in regulating the output voltage to a constant level.
Innovation Solution
Implementing a feedback control circuit with dual control loops, including a slow control loop without or with minimal output ripple and a fast control loop with injected ripple components, using a constant on-time control scheme and a ripple generation circuit to minimize output voltage ripple and enhance accuracy and transient response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional feedback control circuit with single control loop is used, then the circuit structure is simple, but the output voltage accuracy is reduced due to voltage offset from output ripple
Solution Approach 1:
The feedback control circuit is divided into two separate control loops: a first control loop that processes feedback voltage with ripple for fast transient response, and a second control loop that processes filtered feedback voltage for accurate DC voltage regulation. This segmentation allows each loop to specialize in different aspects of voltage control, resolving the contradiction between accuracy and simplicity.
Solution Approach 2:
A ripple filter circuit is introduced as an intermediary component to separate the ripple component from the feedback voltage. The filter allows the first control loop to access the ripple-containing signal for fast response while directing the filtered signal to the second control loop for accurate regulation, thereby eliminating voltage offset without requiring complete redesign of the control architecture.
2Speed
If a conventional single control loop is used, then the control circuit is simple, but the transient response speed is slow when regulating output voltage to constant level
Solution Approach 1:
The control system is segmented into two parallel loops with different response characteristics. The first control loop processes the full feedback voltage including ripple components, enabling fast transient response to load changes. The second control loop handles the filtered DC component for steady-state accuracy. This segmentation allows the system to achieve both fast transient response and simple overall structure.
Solution Approach 2:
The first control loop utilizes the periodic ripple signal inherent in switching regulator operation to detect and respond to transient load changes. By incorporating the ripple-containing feedback voltage into the control decision, the system achieves faster transient response without adding complex external signaling mechanisms, maintaining structural simplicity.
3Speed
If output ripple is present in feedback voltage, then the control loop can respond to transients faster, but voltage offset occurs reducing output voltage accuracy
Solution Approach 1:
The feedback voltage is segmented into two processing paths: one path preserves the ripple component for fast transient detection by the first control loop, while the other path filters the ripple to provide accurate DC voltage information to the second control loop. This segmentation resolves the contradiction by allowing each control loop to operate with the type of signal best suited for its function.
Solution Approach 2:
The ripple filter circuit acts as an intermediary that selectively processes the feedback voltage signal. It allows the first control loop to receive the unfiltered signal with ripple for fast response while simultaneously providing the filtered signal to the second control loop for accurate voltage regulation, thereby eliminating voltage offset while preserving transient response capability.
Data Source
AI summary
A buck switching regulator includes a feedback control circuit including a first gain circuit configured to generate a first feedback signal indicative of the regulated output voltage; a ripple generation circuit configured to generate a ripple signal using the switching output voltage and to inject the ripple signal to the first feedback signal; a second gain circuit configured to generate a second feedback signal indicative of the regulated output voltage; an operational transconductance amplifier (OTA) configured to generate an output signal having a magnitude indicative the difference between the second feedback signal and the first reference signal; and a comparator configured to generate a comparator output signal having an output level indicative of the difference between the output signal of the OTA and the first feedback signal. As thus configured, the buck switching regulator generates an output voltage with increased accuracy and fast transient response.