DC-DC Regulator Light-Load Control for Low Ripple Stability

Solution Overview

Problem

Conventional DC/DC switching mode power supplies face issues with high output voltage ripple and subharmonic oscillation at high duty-cycle and continuous inductor current conditions during light load operation, while attempting to reduce quiescent current, which can be inefficient and lead to undesirable characteristics.

Innovation Solution

The solution involves a DC-DC switching mode power supply circuit that adjusts its switching frequency and modifies the slope compensation ramp signal based on load conditions, maintaining a constant peak inductor current and reducing oscillator frequency to stabilize control during light load operations, thereby reducing quiescent current and output voltage ripple.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If burst mode control is used to reduce quiescent current at light load, then quiescent current is reduced, but output voltage ripple increases

Engineering Contradiction:

Improvequiescent currentVSAvoidoutput voltage ripple

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent implements dynamic adjustment of the slope compensation ramp signal based on operating conditions. The slope compensation is modified according to the duty cycle and load conditions, allowing the system to adapt between continuous conduction mode and discontinuous conduction mode. This dynamic adjustment enables the system to maintain stability and reduce output voltage ripple while operating in burst mode at light loads, resolving the contradiction between quiescent current reduction and ripple suppression.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the slope compensation parameter dynamically based on the operating point. By adjusting the slope compensation ramp signal amplitude and timing according to duty cycle thresholds and load conditions, the system can maintain proper current mode control stability while operating in different modes (continuous, discontinuous, and burst mode). This parameter change allows the system to achieve low quiescent current without suffering from excessive output voltage ripple.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If burst mode control is used to reduce quiescent current at light load, then quiescent current is reduced, but subharmonic oscillation occurs at high duty-cycle conditions

Engineering Contradiction:

Improvequiescent currentVSAvoidinductor current stability

Core Design Contradiction:

Loss of energyVSStability of the object's composition

Solution Approach 1:

The patent implements dynamic slope compensation adjustment that adapts to the duty cycle and operating mode. By continuously monitoring the operating conditions and adjusting the slope compensation ramp signal accordingly, the system maintains current mode control stability even at high duty-cycle conditions during burst mode operation. This dynamic adaptation prevents subharmonic oscillation while enabling quiescent current reduction.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses feedback mechanisms to monitor the inductor current and duty cycle conditions. The slope compensation circuit receives feedback about the operating state and adjusts the compensation signal accordingly. This feedback control ensures that sufficient slope compensation is provided to prevent subharmonic oscillation while allowing the system to operate efficiently in burst mode at light loads.

Inventive Principle:

Principle #23Feedback

3Stability of the object's composition

If smaller inductors are used to avoid subharmonic oscillation, then stability is improved, but efficiency decreases and quiescent current increases

Engineering Contradiction:

Improveinductor current stabilityVSAvoidefficiency

Core Design Contradiction:

Stability of the object's compositionVSLoss of energy

Solution Approach 1:

The patent implements dynamic slope compensation adjustment that adapts to the duty cycle and operating mode. By continuously monitoring the operating conditions and adjusting the slope compensation ramp signal accordingly, the system maintains current mode control stability even at high duty-cycle conditions during burst mode operation. This dynamic adaptation prevents subharmonic oscillation while enabling quiescent current reduction.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses feedback mechanisms to monitor the inductor current and duty cycle conditions. The slope compensation circuit receives feedback about the operating state and adjusts the compensation signal accordingly. This feedback control ensures that sufficient slope compensation is provided to prevent subharmonic oscillation while allowing the system to operate efficiently in burst mode at light loads.

Inventive Principle:

Principle #23Feedback

Data Source

PatentEP3641118B1Regulator light load control techniques

Publication Date: 2023.12.13 ANALOG DEVICES INT UNLTD CO

Figure 1
Figure 2
Figure 3A

AI summary

Techniques for operating a power supply under light load conditions are provided. In an example, a frequency of an oscillator can be adjusted based on a feedback signal indicative of a voltage error of the power supply when the feedback signal falls below a first threshold. In certain examples, a peak inductor current command can be kept constant and a slope compensation ramp can be based on the frequency of the oscillator when the feedback signal falls below the first threshold. In some examples, various circuits of the power supply can be disabled when the feedback signal further falls below a second threshold. The feedback signal can be indicative of a load on the power supply.