Hysteretic DC-DC Converter Observer Circuit Transient Response

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Solution Overview

Problem

Conventional hysteretic DC-DC converters face limitations in transient response due to reduced system gain and bandwidth requirements for stability, which restricts their ability to respond quickly to changes in load current without compromising stability.

Innovation Solution

Incorporating an observer circuit that differentiates the output voltage to generate an observer control signal, which is injected into the control loop, providing output current feed-forward information to enhance transient response and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If system gain and bandwidth are reduced to ensure stability, then phase margin is improved, but transient response deteriorates

Engineering Contradiction:

Improvephase marginVSAvoidtransient response

Core Design Contradiction:

Stability of the object's compositionVSSpeed

Solution Approach 1:

The control system is segmented into two independent parts: the original hysteretic control loop and the added observer circuit. The observer circuit independently generates a feedforward signal that does not interfere with the stability of the main loop, allowing transient response improvement without compromising phase margin.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The observer circuit performs preliminary action by differentiating the output voltage to predict load current changes before they fully manifest. This feedforward signal is injected into the control loop in advance, enabling the converter to respond faster to transient load changes while the main hysteretic loop maintains stability.

Inventive Principle:

Principle #10Preliminary action

2Speed

If system gain is increased to improve transient response, then speed is improved, but stability deteriorates

Engineering Contradiction:

Improvetransient responseVSAvoidphase margin

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The observer circuit acts as an intermediary that provides load current information to the control loop without requiring increased system gain. By differentiating output voltage to generate a feedforward signal, the observer enables fast transient response while the main hysteretic comparator maintains adequate phase margin and stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Speed

If loop bandwidth is increased to improve transient response, then speed is improved, but noise immunity deteriorates

Engineering Contradiction:

Improveloop bandwidthVSAvoidnoise immunity

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The control architecture is segmented such that the observer circuit operates independently with its own differentiation and amplification stages. This allows the observer to provide fast transient response with higher effective bandwidth while the main hysteretic loop maintains lower bandwidth for noise immunity. The two segments work together without the noise penalties of a single high-bandwidth system.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS8138739B1Circuits and methods for improving transient response of hysteretic DC-DC converters

Publication Date: 2012.03.20 SEMICON COMPONENTS IND LLC

AI summary

A hysteretic DC-DC converter includes an observer circuit configured to generate an observer control signal for injection into the control loop of the converter. The observer circuit may be configured to differentiate the output voltage of the converter to generate a differentiated output voltage. A transconductance amplifier may be configured to output the observer control signal from the differentiated output voltage. The observer control signal may be injected into the control loop in a summing node.