Open-Loop Resonant Converter Dimming via Frequency Modulation
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Solution Overview
Problem
Existing open-loop resonate converters face limitations in dimming control, particularly at extremely low dimming levels where the 'OFF' periods are longer, affecting voltage range and dimming accuracy, and the controller is not easily powered by the auxiliary winding, especially in PWM-based dimming systems.
Innovation Solution
An open-loop resonate converter that modulates the switching frequency of the resonant tank between a first fixed frequency and a second fixed frequency based on a dimming control signal, using a voltage or current controlled oscillator to adjust the duty cycle, ensuring adequate energy transfer and powering the controller even at high dimming conditions, thereby implementing PFM-based dimming without the need for a separate PWM dimming pin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM-based dimming is implemented in open-loop resonate converters, then dimming control is achieved, but the controller cannot be easily powered by the auxiliary winding at extremely low dimming conditions and the voltage range operating window is limited
Solution Approach 1:
The patent implements dynamic frequency switching between two fixed frequencies (first fixed frequency and second fixed frequency) based on dimming control signals. The resonant tank switches between these frequencies to maintain adequate power transfer to the auxiliary winding even at extreme dimming levels, ensuring continuous controller operation. This dynamic adaptation resolves the contradiction by making the system flexible rather than static.
Solution Approach 2:
The patent changes the switching frequency parameter of the resonant tank between two fixed values depending on the dimming level. By switching between first fixed frequency and second fixed frequency based on the dimming control signal, the system maintains adequate power transfer to the auxiliary winding across all dimming conditions, including extreme low dimming levels where PWM-based dimming fails to provide sufficient power.
2Illumination intensity
If PWM-based dimming is used, then luminance control is achieved, but blanking time during mode transient limits the voltage range operating window and affects dimming accuracy
Solution Approach 1:
The patent extracts and eliminates the blanking time requirement inherent in PWM-based dimming by using frequency switching instead of pulse width modulation. The resonant tank operates continuously at one of two fixed frequencies, removing the need for blanking periods during mode transitions. This extraction of the problematic blanking time element resolves the contradiction between luminance control and dimming accuracy.
3Use of energy by moving object
If the resonant tank switches at higher frequency, then energy transfer is improved, but constant LED current is not provided over the voltage range
Solution Approach 1:
The patent dynamically switches between two fixed frequencies based on operating conditions. At normal operation, the resonant tank operates at the first fixed frequency to provide constant LED current. When higher energy transfer is needed (such as at extreme dimming levels), it switches to the second fixed frequency. This dynamic frequency selection resolves the contradiction by allowing the system to adapt to different operational requirements.
Solution Approach 2:
The patent uses periodic switching between two fixed frequencies based on dimming control signals. The resonant tank alternates between first fixed frequency and second fixed frequency operation in response to dimming levels, enabling adequate energy transfer during high dimming conditions while maintaining constant LED current during normal operation. This periodic action between two frequency states resolves the contradiction.
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 improved dimming control and maintains a minimum voltage at the auxiliary winding for powering the controller across a wider range of dimming conditions, ensuring reliable operation and accurate dimming without the limitations of conventional PWM dimming.
Implementation Method 1
a transformer having a first winding on a primary side of the open-loop resonate converter and a second winding on a secondary side of the open-loop resonate converter; a resonant tank coupled to the first winding of the transformer
Implementation Method 2
a resonant tank coupled to the first winding of the transformer and configured, at a first fixed frequency, to provide a constant LED current over a voltage range at the secondary side without feedback from the secondary side
Data Source
AI summary
An open-loop resonate converter includes: a transformer having a first winding on a primary side of the open-loop resonate converter and a second winding on a secondary side of the open-loop resonate converter; a resonant tank coupled to the first winding of the transformer and configured, at a first fixed frequency, to provide a constant LED current over a voltage range at the secondary side without feedback from the secondary side; and a circuit configured to modulate switching of the resonant tank between the first fixed frequency and a second fixed frequency higher than the first fixed frequency based on a dimming control signal input to the circuit, such that the resonant tank is switched at the first fixed frequency for longer durations when the dimming control signal indicates less dimming and for shorter durations when the dimming control signal indicates more dimming.