LED Driver Circuit PWM Modulation and Frequency Control
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Solution Overview
Problem
Existing driver circuits for LEDs face challenges in precisely controlling LED current and brightness due to limitations in PWM modulation resolution and the uncertainty of magnetizing current in LLC resonant converter topology, leading to approximate brightness setting and color inconsistency.
Innovation Solution
A driver circuit with a control loop that continuously modulates the manipulated variable using PWM signals, even during switch-off periods, and incorporates a low-pass filter to set a slower time constant, allowing for independent duty cycle adjustment and improved color constancy by maintaining constant LED current during PWM modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If low-frequency PWM modulation is used to dim LED sections, then dimming capability is achieved, but PWM modulation resolution is limited causing dithering and imprecise frequency control
Solution Approach 1:
The patent segments the dimming control into two independent parts: PWM modulation for dimming capability and high-resolution frequency control for precision. The PWM signal controls the on/off timing while the frequency controller independently adjusts the LLC converter frequency, allowing both functions to operate optimally without interference.
Solution Approach 2:
The patent introduces an intermediary frequency control mechanism that acts between the PWM signal and the LLC converter. This intermediary controller receives the PWM dimming command and translates it into precise frequency adjustments, mediating between the coarse PWM timing and the fine frequency control requirements.
2Device complexity
If primary-side current measurement is used for constant control, then control simplicity is maintained, but measurement accuracy deteriorates due to magnetizing current uncertainty
Solution Approach 1:
The patent implements a feedback mechanism where the actual LED current is continuously measured and compared with the target current. The controller adjusts the frequency based on this feedback to minimize the difference, ensuring accurate current control despite the complexities of magnetizing current in the LLC topology.
Solution Approach 2:
The patent replaces direct primary-side current measurement with an alternative approach using frequency control. Instead of directly measuring and controlling primary current, the system controls the switching frequency to indirectly achieve the desired LED current, substituting a mechanical measurement problem with a frequency-based control solution.
3Measurement precision
If lookup table correction is used to compensate for magnetizing current, then measurement correction is achieved, but device complexity increases and only approximate correction is possible
Solution Approach 1:
The patent changes the control parameter from direct current measurement correction to frequency control. Instead of attempting to correct current measurements using lookup tables, the system adjusts the switching frequency as the control parameter, which inherently compensates for magnetizing current effects without requiring complex correction circuits.
4Illumination intensity
If PWM modulation is used for dimming, then brightness control is achieved, but color consistency deteriorates due to current variation during modulation
Solution Approach 1:
The patent ensures continuous useful action by maintaining constant LED current during PWM modulation periods. The frequency controller continuously adjusts the LLC converter frequency even during PWM off-times, ensuring the LED current remains stable and preventing color shifts that would occur with current variation.
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 solution enables precise control of LED brightness and improved color consistency by maintaining constant LED current over PWM modulation periods, overcoming the limitations of existing technologies.
Implementation Method 1
a resonant circuit, such as an LLC converter, which is responsible for transferring current across a galvanic barrier from a primary side to a secondary side of the barrier
Implementation Method 2
incorporates a low-pass filter to set a slower time constant, allowing for independent duty cycle adjustment and improved color constancy by maintaining constant LED current during PWM modulation
Data Source
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AI summary
The invention relates to a driver circuit (1) for lamps, in particular for one or more LEDs, comprising: - a circuit (2) that can be supplied with a voltage (Vdc) and is clocked by means of at least one switch (LS, HS), which circuit feeds a resonance circuit (3) serving to supply the lamps with current, - a control circuit for controlling the lamp current has a controller (10), wherein the controller (10), depending on a feedback signal (Im) that reproduces the current through the lamp, and depending on a signal (ILS) that reproduces a target value for the lamp current, generates a target value (ASF) for controlling the lamp current, - a PWM modulator (11) for modulating the target value (ASF) with a PWM signal.