Hysteretic Regulator for LED Current Control
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Solution Overview
Problem
Fixed-frequency PWM control techniques in LED power supply systems require loop compensation, leading to limited system response and increased circuit complexity, while resistive sense elements cause power losses due to continuous operation, especially when driving high-power LEDs.
Innovation Solution
The implementation of balanced hysteretic control (BHC) in a regulator circuit, which includes a current sensing element, a true average current control unit, and a hysteretic control unit, allows for fast response and low-loss sensing by dynamically adjusting peak and valley currents through an inductor, reducing power losses by only activating the current sensing element during switch conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If fixed-frequency PWM control technique is used, then the regulator can control the voltage supplied to LED string, but the system response is limited and circuit complexity increases due to loop compensation requirement
Solution Approach 1:
The patent implements dynamic switching frequency adjustment where the switching frequency varies based on the difference between actual and target LED currents. The controller dynamically modifies the switching frequency within a predetermined range, eliminating the need for fixed-frequency PWM and its associated loop compensation circuits, thereby reducing circuit complexity while maintaining fast response.
Solution Approach 2:
The patent employs a feedback mechanism where the actual LED current is continuously monitored and compared with the target current. Based on this comparison, the controller dynamically adjusts the switching frequency to minimize the current difference, achieving fast response without requiring complex loop compensation typically needed in fixed-frequency PWM systems.
2Measurement precision
If resistive sense element is coupled in series with LED string for current sensing, then the current can be measured, but power losses increase during entire operating period
Solution Approach 1:
The patent implements periodic current sensing where the resistive sense element is only activated during specific switching intervals rather than continuously. The controller periodically switches the sense element in and out based on the switching cycle, enabling current measurement when needed while minimizing power dissipation during non-sensing periods, thus reducing overall power losses.
Solution Approach 2:
The patent dynamically controls the activation state of the resistive sense element, switching it between active and inactive states based on the operating conditions. During intervals when current measurement is not required, the sense element is deactivated, eliminating unnecessary power dissipation while maintaining measurement capability when needed.
3Measurement precision
If resistive sense element operates continuously to sense current, then accurate current control is achieved, but efficiency reduces due to constant power dissipation
Solution Approach 1:
The patent implements periodic current sensing where the resistive sense element is only activated during specific switching intervals rather than continuously. The controller periodically switches the sense element in and out based on the switching cycle, enabling current measurement when needed while minimizing power dissipation during non-sensing periods, thus reducing overall power losses.
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
This approach achieves true average current control with reduced power losses and improved efficiency, especially when driving high-power LEDs, by dynamically adjusting currents and minimizing the time the current sensing element is active.
Implementation Method 1
The current flows through the resistive sense element, generating a voltage that can be compared to a reference voltage
Implementation Method 2
a switched mode regulator generates a supply voltage for the LED string
Data Source
AI summary
An apparatus includes a sense element that generates a sense signal based on an output signal generated by a regulator. The apparatus also includes a current control unit that generates a compensated reference signal using the sense signal. The compensated reference signal is associated with an average of the output signal. The apparatus further includes a comparator that compares the compensated reference signal and the sense signal. In addition, the apparatus includes a hysteretic control unit that adjusts a control signal based on an output of the comparator and that provides the control signal to the regulator in order to adjust the output signal generated by the regulator. The hysteretic control unit could dynamically adjust peak and valley currents through an inductor in the regulator to maintain the average of the output signal at a substantially constant value.