Double-Edge PWM Controller Transient Response

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Solution Overview

Problem

Existing DC-DC converters using peak current mode control face significant delays in responding to load variations due to PWM being set HIGH only at the leading edge, which limits their ability to quickly respond to transient changes in load.

Innovation Solution

The implementation of double-edge pulse width modulation (PWM) control, where PWM is triggered at both edges and modulated in real-time by both output current and voltage, using a circuit with a switch element, filtering elements, and feedback mechanisms to ensure quicker transient response.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If peak current mode control with leading-edge PWM is used, then the control structure is simple and linear modulation is good, but the transient response to load variation is slow with delay up to (1-D)*T

Engineering Contradiction:

Improvecontrol structureVSAvoidtransient response delay

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The PWM control cycle is segmented into two independent edges: leading-edge PWM and trailing-edge PWM. Each edge independently controls one switching cycle, allowing the system to respond to load variations at both edges rather than waiting for the next leading edge, thus reducing the maximum response delay from (1-D)*T to approximately 0.5T

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The trailing-edge PWM signal is generated in advance based on predicted load conditions and feeds forward to pre-adjust the duty cycle for the next leading edge. This preliminary action allows the system to anticipate and prepare for load variations before they fully manifest, reducing response delay

Inventive Principle:

Principle #10Preliminary action

2Loss of time

If double-edge PWM control is implemented to reduce response delay, then transient response speed improves, but noise sensitivity increases requiring additional suppression circuits

Engineering Contradiction:

Improveresponse delayVSAvoidnoise sensitivity

Core Design Contradiction:

Loss of timeVSObject-affected harmful factors

Solution Approach 1:

The noise introduced by double-edge PWM is converted into a manageable parameter through feedforward compensation. The trailing-edge PWM signal, which could be seen as a source of noise and instability, is actually used predictively to pre-adjust the leading-edge duty cycle, transforming potential harm into a beneficial predictive control mechanism

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

A feedback mechanism is implemented where the actual output current and voltage are continuously monitored and used to adjust both leading-edge and trailing-edge PWM signals. This closed-loop feedback compensates for noise effects while maintaining the fast transient response benefits of double-edge control

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7880522B2Double-edge PWM controller and its control method thereof

Publication Date: 2011.02.01 MONOLITHIC POWER SYSTEMS INC

AI summary

The present invention discloses a double-edge pulse width modulation (PWM) controller based on the output current and output voltage which is modulated in real time by the output current and the output voltage. The controller uses an extra first adder to sum up the compensation signal and a triangular signal (or a saw-tooth signal); a second adder to sum up the output current signal to a bias value; a PWM comparator, with its non-inverting input receiving the output of said first adder, its inverting input receiving the output of said second adder and outputs the PWM signal.