Buck DC-DC Converter Ripple Injection Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional buck switching regulators experience voltage offset and reduced accuracy due to output ripple, which degrades load regulation and PSRR performance, especially when using low ESR capacitors that do not generate sufficient ripple for feedback control.
Innovation Solution
The implementation of an accuracy enhanced feedback network with a ripple generation circuit and a balanced feedback network that injects ripple signals into both feedback circuits to correct for voltage offsets and improve stability, allowing for the use of low ESR capacitors and enhancing output voltage accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low ESR capacitors are used in the output filter circuit, then power loss is reduced and efficiency is improved, but output ripple voltage becomes insufficient for feedback control and voltage accuracy deteriorates
Solution Approach 1:
The feedback control system is segmented into two parallel paths: one path uses the traditional feedback voltage for control, while the second path uses a replicated feedback circuit to generate a ripple signal. This segmentation allows the low ESR capacitor to be used without compromising feedback control capability, as the ripple is now generated by the replicated circuit rather than relying on capacitor ESR.
Solution Approach 2:
An ripple generation circuit is introduced as an intermediary component that receives the replicated feedback voltage and generates the necessary ripple signal. This intermediary circuit bridges the gap between using low ESR capacitors (which minimize ripple) and maintaining sufficient ripple for accurate feedback control, allowing both requirements to be satisfied simultaneously.
2Reliability
If output ripple is used for feedback control, then voltage regulation is achieved, but voltage offset is introduced and accuracy is reduced
Solution Approach 1:
A replicated feedback circuit is created as a copy of the original feedback path. This copy generates a ripple signal that is free from the DC offset present in the main feedback voltage. The offset-free ripple from the copied circuit is then used for control, maintaining voltage regulation accuracy while eliminating the offset error that would otherwise degrade precision.
Solution Approach 2:
The ripple signal is extracted from the replicated feedback circuit separately from the main feedback voltage path. By taking out the ripple component through the replicated circuit, the system can utilize ripple for control purposes without introducing offset errors into the primary voltage regulation loop, thus maintaining both regulation and accuracy.
3Device complexity
If conventional feedback control is used with low ESR capacitors, then device complexity is reduced, but stability and load regulation performance deteriorate
Solution Approach 1:
The replicated feedback circuit serves multiple functions: it generates the ripple signal needed for feedback control, provides an offset-free reference, and improves loop stability. This multi-functionality allows the system to achieve better stability and load regulation performance without proportionally increasing device complexity, as the same replicated circuit structure accomplishes multiple objectives simultaneously.
Data Source
AI summary
A buck switching regulator includes a feedback control circuit including a balanced feedback network including first and second gain circuits configured to generate first and second feedback signals, respectively, indicative of the regulated output voltage; a ripple generation circuit configured to inject a first ripple signal to the first gain circuit and a second ripple signal to the second gain circuit; an operational transconductance amplifier (OTA) configured to receive the second feedback signal and a reference signal and to generate an output signal being coupled to a node in the feedback control circuit; and a comparator configured to receive the first feedback signal and a comparator reference signal and to generate a comparator output signal. The output signal of the OTA is applied to the feedback control circuit to cancel a voltage offset in the regulated output voltage due to the injected ripple signal to the first gain circuit.