Half-Bridge Resonant LED Driver With PWM Dimming Feedback
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Solution Overview
Problem
Self-oscillating LED drivers with resonant circuits face challenges in adjusting output current and light output, making it difficult to achieve precise dimming and frequency variation compared to externally controlled circuits.
Innovation Solution
An operating circuit with a half-bridge circuit and series resonant circuit, where high-frequency clocking is superimposed with low-frequency PWM modulation, allowing for adjustable duty cycle and feedback control to regulate current through the LED load, using a microcontroller or ASIC for control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional LED driver circuit with separate control and drive circuits is used, then the circuit can drive LED loads, but the circuit complexity increases and integration density decreases
Solution Approach 1:
The patent combines the control circuit and drive circuit into a single integrated circuit device. The control circuit includes a controller that generates control signals, and the drive circuit includes a half-bridge circuit with switching elements that are controlled by these signals. Both circuits share a common reference potential, eliminating the need for separate control and drive circuit boards, thereby reducing overall circuit complexity while maintaining integration density.
Solution Approach 2:
The integrated circuit is designed to drive multiple types of LED loads including series-connected LEDs, parallel-connected LEDs, and strings of series-connected parallel-connected LEDs. The half-bridge circuit can operate in different configurations (full bridge or half bridge) depending on the load requirements, providing universal functionality across different LED configurations while maintaining a single integrated structure.
2Ease of manufacture
If separate control and drive circuits are used with different reference potentials, then each circuit can be optimized independently, but the number of components increases and integration is reduced
Solution Approach 1:
The control circuit and drive circuit are merged into a single integrated circuit with a common reference potential. The controller and half-bridge circuit share the same ground reference, eliminating the need for separate reference potential circuits and reducing the total number of components. This unified structure simplifies manufacturing while maintaining the ability to optimize control and drive functions within the same device.
3Adaptability or versatility
If a half-bridge circuit with body diodes of switching elements is used, then the circuit can drive various LED configurations, but reverse current through body diodes causes efficiency loss
Solution Approach 1:
The patent addresses the efficiency loss from body diode conduction by implementing a body diode compensation circuit. This circuit detects when body diodes are conducting reverse current and actively compensates for the energy loss by injecting compensating current or adjusting switching timing. The harmful effect of body diode conduction is converted into a manageable parameter through active compensation, maintaining both LED configuration compatibility and driving efficiency.
Solution Approach 2:
The body diode compensation circuit uses feedback mechanisms to monitor the conduction state of body diodes and adjust the driving signals accordingly. When reverse current flows through body diodes, the feedback signal triggers compensation actions that prevent energy loss. This feedback control enables the circuit to maintain high efficiency across different LED configurations while preserving the versatility of the half-bridge topology.
4Speed
If the switching frequency of the half-bridge circuit is increased to improve response time, then dynamic performance improves, but switching losses increase
Solution Approach 1:
The patent implements dynamic switching frequency control where the switching frequency of the half-bridge circuit is adjusted based on operating conditions. During transient states requiring fast response, the switching frequency is increased to improve response time. During steady-state operation, the frequency is reduced to minimize switching losses. This dynamic adjustment optimizes both response time and efficiency across different operating scenarios.
Solution Approach 2:
The controller dynamically changes the switching frequency parameter based on load conditions and desired performance. When fast response is required, the frequency parameter is increased; when efficiency is prioritized, the frequency parameter is decreased. This parameter optimization allows the system to achieve the desired balance between response time and switching losses by adapting the frequency to specific operational requirements.
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
Enables precise control over LED current and dimming, allowing for flexible frequency operation and efficient dimming across various dimming ranges, improving the adjustability of LED output current and light intensity.
Implementation Method 1
a series resonant circuit, in particular an LLC resonant circuit, is supplied from a midpoint of the two switches
Implementation Method 2
A transformer is also provided, whose stray inductance is part of the resonant circuit or is connected in series with a discrete resonant choke, and whose secondary side supplies terminals for an LED load
Data Source
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AI summary
The invention relates to an operating circuit (BS) for an LED load, comprising: a half-bridge circuit (HB) comprising two switches (HS, LS) connected in series; a series-resonant circuit supplied from the midpoint of the two switches (HS, LS); a transformer (GT), the leakage inductance of which is part of the resonant circuit, or which is arranged in series with a discrete resonant choke and from the secondary side of which connections for an LED load (LED) are supplied; and a control circuit (ST) which clocks the switch (HS, LS) of the half bridge at a high frequency, wherein the control circuit (ST) of the high-frequency clocking superimposes a PWM modulation at a low frequency in comparison thereto, wherein the high-frequency clocking can be adjusted by means of forward supervision, and the pulse duty factor of the PWM modulation is modified by means of feedback control, wherein, for the feedback control, a signal reproducing a current through the LED is supplied to the control circuit (ST).