Open Loop Ripple Cancellation in DC-DC Converters

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Solution Overview

Problem

Switching power supplies face challenges in minimizing and mitigating ripple current, which is undesirable and can affect the load, due to varying inductance caused by manufacturing tolerances and temperature drift.

Innovation Solution

A DC-DC converter with an open loop ripple cancellation circuit and a parallel amplifier, which operates in calibration and normal modes to estimate and cancel ripple current, using a switching control signal to drive the parallel amplifier output current toward zero and update the current gain to compensate for inductance changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a switching supply uses an inductive element to translate input voltage to output voltage, then power conversion is achieved, but ripple current is generated which is harmful to the load

Engineering Contradiction:

Improvepower conversion capabilityVSAvoidripple current

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent measures the harmful ripple current generated by the switching supply and uses it as a reference signal to drive a parallel amplifier that generates a canceling current. The harmful ripple current is converted into a useful reference for creating its own cancellation, effectively turning the problem into a solution.

Inventive Principle:

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

Solution Approach 2:

The patent introduces a parallel amplifier as an intermediary component that receives the ripple current signal and generates a compensating current. This intermediary element mediates between the switching supply and the load, canceling the harmful effects of ripple current without disrupting the power conversion function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the inductance of the inductive element changes due to manufacturing tolerances and temperature drift, then the ripple current characteristics change, but the ripple cancellation effectiveness deteriorates

Engineering Contradiction:

Improveinductance variation toleranceVSAvoidripple cancellation effectiveness

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent employs feedback by continuously measuring the actual ripple current generated by the switching supply and using this measurement to adjust the parallel amplifier's output. This closed-loop approach ensures that the ripple cancellation adapts to changes in inductance due to temperature drift or manufacturing variations, maintaining effectiveness under varying conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent includes a calibration mode that performs preliminary adjustment of the ripple cancellation circuit before normal operation. During calibration, the system determines optimal cancellation parameters based on the actual inductance value, preparing the system to handle subsequent inductance variations during normal operation.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If a calibration mode is implemented to determine current gain and compensate for inductance changes, then ripple cancellation accuracy is improved, but device complexity increases

Engineering Contradiction:

Improvecurrent gain accuracyVSAvoidcalibration circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent combines the calibration functionality with the existing ripple cancellation circuit by using the same parallel amplifier and control infrastructure. The calibration mode leverages existing components rather than adding completely separate calibration hardware, thereby reducing the increase in device complexity while still achieving accurate current gain determination.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS9225231B2Open loop ripple cancellation circuit in a DC-DC converter

Publication Date: 2015.12.29 QORVO US INC

AI summary

A direct current (DC)-DC converter, which includes an open loop ripple cancellation circuit, a switching supply, and a parallel amplifier, is disclosed. During a calibration mode, the parallel amplifier provides a parallel amplifier output current to regulate a power supply output voltage based on a calibration setpoint. The switching supply drives the parallel amplifier output current toward zero using a switching control signal, such that during the calibration mode, an estimate of a current gain is based on the switching control signal. Further, during the calibration mode, the open loop ripple cancellation circuit is disabled. During a normal operation mode, the open loop ripple cancellation circuit provides a ripple cancellation current, which is based on the estimate of the current gain.