Buck-Boost LED Driver Current Regulation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional LED lighting systems using buck-boost topology suffer from instability and flickering due to variations in output current caused by conventional controller designs, which are sensitive to input voltage changes.

Innovation Solution

A buck-boost pulse width modulation (PWM) power supply system with an analog signal processor that senses input and output voltages to maintain a constant output current, using a transconductance amplifier, comparator, and power MOSFET to regulate current flow, and includes safety features like over-voltage and over-current protection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional CCM or VCM loop control is used in buck-boost topology, then the power supply can operate, but circuit instability and flickering occur

Engineering Contradiction:

Improvecircuit stabilityVSAvoidoperation stability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent implements a current feedback mechanism where the current through the LED string is sensed and fed back to the control circuit. This feedback loop allows the controller to adjust the switching duty cycle dynamically to maintain constant current, eliminating the instability and flickering problems associated with conventional CCM or VCM loop control.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces conventional voltage-based control mechanisms with a current-based control system. By sensing current directly and using it as the primary control parameter, the system achieves more stable operation compared to voltage control methods that are prone to instability in buck-boost topology.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If conventional controllers sensitive to input voltage changes are used, then the power supply can adapt to voltage variations, but output current varies causing instability

Engineering Contradiction:

Improveinput voltage adaptabilityVSAvoidoutput current stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent uses current sensing feedback to maintain constant output current regardless of input voltage variations. The sensed current is compared with a reference, and the error signal adjusts the switching duty cycle to compensate for input voltage changes, ensuring stable output current while adapting to varying input conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the control parameter from voltage-based to current-based control. By making output current the primary controlled parameter rather than output voltage, the system achieves both adaptability to input voltage changes and stability in output current, resolving the contradiction between these two requirements.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If switching mode power supply is used instead of linear regulator, then size and efficiency improve, but electromagnetic interference increases

Engineering Contradiction:

Improvepower efficiencyVSAvoidelectromagnetic interference

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent employs current-mode control with feedback that operates at a fixed frequency, which helps reduce electromagnetic interference compared to voltage-mode control. The feedback mechanism ensures clean switching transitions and reduces noise generation while maintaining the high efficiency benefits of switching mode operation.

Inventive Principle:

Principle #23Feedback

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 system provides a stable and constant output current to LEDs, preventing flickers and ensuring consistent light output, even with variations in input voltage, and includes safety features for protection against over-voltage, over-current, and over-temperature conditions.

Implementation Method 1

a transconductance amplifier circuit for receiving a voltage signal related to a current from an input of the power supply and providing a first signal

Methodology Applied

Scientific EffectTransconductance amplification:

Implementation Method 2

a power transistor for controlling current flow in the power supply based on a control signal from the control circuit

Methodology Applied

Scientific EffectMOSFET switching:

Implementation Method 3

buck-boost pulse width modulation (PWM) power supply

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS8344656B2Methods and systems for LED driver having constant output current

Publication Date: 2013.01.01 BCD (SHANGHAI) MICRO ELECTRONICS LTD

AI summary

A control circuit for a switched mode power supply includes a transconductance amplifier circuit for receiving a voltage signal related to a current from an input of the power supply and producing a first signal, an analog signal processor coupled to the amplifier circuit for receiving the first signal and a second signal from the input of the power supply and a third signal from an output of the power supply. The analog signal processor is configured to produce a fourth signal as a function of the first, the second, and the third signals. An adder circuit is coupled to the fourth signal and a dimmer control signal, and the adder circuit is configured to output a fifth signal. A comparator circuit is coupled to the adder circuit for providing a control signal to a power transistor that controls current flow in the power supply based on comparison of the fifth signal and a reference signal.