Switch Mode Power Supply Control Circuit for Light Load Efficiency

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Solution Overview

Problem

Conventional constant on-time controlled switch mode power supplies face inefficiencies at light loads due to increased power loss and driving loss with higher switching frequencies, which hampers the standby time of electronic devices in always-on and always-connected modes.

Innovation Solution

A control circuit for switch mode power supplies that adjusts the on-time period of the first switch based on input and output voltages, transitioning to a power saving mode at light loads to reduce switching frequency and enhance efficiency, while maintaining fast transient response at normal loads.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If higher switching frequency is used to achieve faster load transient response and smaller size, then the switching frequency increases, but driving loss and switching loss increase at light load

Engineering Contradiction:

Improveload transient response speedVSAvoiddriving loss and switching loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The patent implements dynamic switching frequency adjustment by introducing a mode control signal that switches between power saving mode and normal mode. In power saving mode, the on-time period is extended to reduce switching frequency at light load, thereby reducing driving loss and switching loss. In normal mode, the on-time period returns to conventional values to maintain fast load transient response. This dynamic adjustment resolves the contradiction between fast response and energy efficiency.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the on-time period parameter based on load conditions and mode control signal. By adjusting the on-time period duration, the switching frequency is indirectly controlled. In power saving mode, the extended on-time period reduces switching frequency to minimize power loss. This parameter change strategy enables the system to adapt to different operating conditions and resolve the trade-off between response speed and energy efficiency.

Inventive Principle:

Principle #35Parameter changes

2Weight of stationary object

If higher switching frequency is used to achieve smaller size and weight, then the switching frequency increases, but power loss increases at light load

Engineering Contradiction:

Improvepower supply size and weightVSAvoidpower loss

Core Design Contradiction:

Weight of stationary objectVSLoss of energy

Solution Approach 1:

The patent employs dynamic mode switching between power saving mode and normal mode based on load conditions. In power saving mode, the extended on-time period reduces switching frequency, which directly reduces power loss at light load. This dynamic adaptation allows the system to maintain compact size while minimizing power consumption during standby and light load operations.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent adjusts the on-time period parameter dynamically to control switching frequency. By extending the on-time period in power saving mode, the switching frequency is reduced, thereby reducing power loss. This parameter adjustment mechanism enables the power supply to achieve both compact size and low power loss under different operating conditions.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If conventional constant on-time control is used to maintain simple internal configuration, then the control circuit remains simple, but efficiency at light load deteriorates

Engineering Contradiction:

Improveinternal configuration complexityVSAvoidefficiency at light load

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent enhances the functionality of the control circuit by adding mode control capability while maintaining the basic constant on-time control structure. The control circuit can operate in both power saving mode and normal mode, making it multi-functional. This allows the system to improve light load efficiency without significantly increasing complexity, as the same control circuit adapts its behavior based on mode control signal and load conditions.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The control circuit implements dynamic mode switching between power saving mode and normal mode based on load conditions. This dynamic behavior allows the circuit to optimize efficiency at light load by extending the on-time period in power saving mode, while maintaining simple operation at full load. The dynamic adaptation improves efficiency without requiring completely separate control circuits for different modes.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS9559586B2Switch mode power supply, control circuit and associated control method

Publication Date: 2017.01.31 CHENGDU MONOLITHIC POWER SYST

AI summary

A switch mode power supply having an output terminal configured to provide an output voltage, the switch mode power supply has a first switch and a control circuit. The control circuit is configured to provide a switching control signal to turn ON and turn OFF the first switch, an on-time period of the first switch is proportional to a first value when the switch mode power supply works in a power saving mode, and the on-time period of the first switch is proportional to a second value when the switch mode power supply works in a normal mode, wherein the first value is larger than the second value.