Isolated Converter Dead Time PWM Delay Control

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Solution Overview

Problem

Conventional synchronous rectifier controllers in power converters face challenges in preventing simultaneous conduction of switches during load variations and startup/shutdown, leading to energy losses and potential damage from voltage spikes due to reverse currents.

Innovation Solution

A power converting device incorporating a PWM controller and synchronous rectifier controller with a dead time mechanism, ensuring the secondary switch is non-conductive before the primary switch conducts, using a transformer with primary and secondary windings and a rectifier-filter circuit to manage conduction and non-conduction, preventing reverse currents and voltage spikes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If synchronous rectifier controller uses capacitor charging/discharging to control switch conduction time, then the controller can operate in both DCM and CCM, but the capacitor response time causes delay in detecting rapid load variations, leading to simultaneous conduction of switches

Engineering Contradiction:

Improveoperating mode adaptabilityVSAvoidload variation response speed

Core Design Contradiction:

Adaptability or versatilityVSSpeed

Solution Approach 1:

The patent introduces a dead time mechanism that proactively turns off the synchronous rectifier switch before the main switch turns on. This preliminary action prevents the simultaneous conduction problem before it can occur, rather than reacting after the capacitor delay causes the issue. The dead time is inserted in the control signal path to ensure the secondary switch is turned off in advance.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses a dead time control circuit as an intermediary between the main switch control and the synchronous rectifier switch control. This intermediary component introduces a time delay that decouples the direct relationship between the two switches, allowing the synchronous rectifier switch to be turned off before the main switch turns on, thus preventing simultaneous conduction.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If synchronous rectifier switch is turned off after output current drops to zero, then the controller can maintain continuous conduction mode operation, but voltage spikes and reverse currents occur during rapid load variations

Engineering Contradiction:

Improvecontinuous conduction capabilityVSAvoidvoltage spike and reverse current

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by turning off the synchronous rectifier switch before the main switch turns on during dead time. This preventive measure counteracts the potential harmful effect of simultaneous conduction and reverse current before they can occur, rather than attempting to mitigate them after they happen.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The dead time mechanism performs a preliminary action of turning off the synchronous rectifier switch in advance before the main switch conducts. This ensures that even if load variations occur rapidly, the secondary switch is already non-conductive, preventing the generation of reverse currents and voltage spikes.

Inventive Principle:

Principle #10Preliminary action

3Adaptability or versatility

If RC trigger is used to forcibly turn off synchronous rectifier circuit, then the controller can operate in CCM, but the RC time constant prevents rapid load variation response

Engineering Contradiction:

ImproveCCM operation capabilityVSAvoidload variation response speed

Core Design Contradiction:

Adaptability or versatilityVSSpeed

Solution Approach 1:

The patent uses dead time control to proactively turn off the synchronous rectifier switch before the main switch turns on, eliminating the need for RC triggers that rely on capacitor charging/discharging. This preliminary action ensures rapid response to load variations without being constrained by RC time constants.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively prevents simultaneous conduction of switches and reverse currents, enhancing circuit stability during load variations and startup/shutdown, thereby reducing energy losses and protecting components from voltage spikes.

Implementation Method 1

the secondary winding generates an induced voltage in response to induction associated with receipt of the input voltage by the primary winding

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS9490716B2Isolated converter with initial rising edge PWM delay

Publication Date: 2016.11.08 LITE ON ELECTRONICS (GUANGZHOU) LTD

AI summary

A power converting device includes a transformer, a first switch coupled to a primary winding of the transformer, a PWM controller which generates a first PWM signal for controlling conduction and non-conduction of the first switch and which generates a control signal that leads the first PWM signal, a rectifier-filter circuit which rectifies an induced voltage generated by a secondary winding of the transformer, a second switch coupled to the secondary winding, and a synchronous rectifier controller which controls conduction and non-conduction of the second switch, and which controls, according to the control signal, the second switch to become non-conductive prior to conduction of the first switch.