Shunt-Dimming LED Driver With Dual-State Power Control
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Solution Overview
Problem
Existing LED drivers face inefficiencies in deep dimming scenarios due to high energy dissipation and uneven brightness variations when using pulse dimming signals with unstable duty cycles, making precise dimming difficult.
Innovation Solution
A control circuit with a shunt switch and dual control circuits to manage power converter operation in normal and low power states based on dimming signals, enabling time-sharing and feedback control for precise dimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse dimming signal with low duty cycle is used for deep dimming, then LED brightness is reduced, but energy efficiency deteriorates due to high energy dissipation
Solution Approach 1:
The patent employs periodic action through two mechanisms: (1) The shunt switch operates periodically to bypass excess current during PWM dimming, and (2) the power converter alternates between normal and low power operation states in time-sharing manner. This periodic operation enables precise control of average current while minimizing energy waste by actively managing current paths and converter states during each PWM cycle.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the operation state of the power converter based on the PWM dimming signal duty cycle. When duty cycle indicates deep dimming is required, the converter switches from normal power operation state to low power operation state, changing its operating parameters to match the reduced power demand and improve efficiency.
2Adaptability or versatility
If pulse dimming signal with unstable duty cycle is used, then dimming range is extended, but brightness uniformity deteriorates
Solution Approach 1:
The patent implements feedback control where the shunt control circuit receives the PWM dimming signal and generates a shunt control signal with inverted duty cycle. This feedback mechanism ensures that the shunt switch operates complementarily to the PWM signal, maintaining stable current distribution and uniform brightness across the LED even when duty cycle varies widely, thereby extending dimming range without sacrificing brightness uniformity.
Solution Approach 2:
The shunt control circuit acts as an intermediary between the PWM dimming signal and the shunt switch. It processes the PWM signal to generate an appropriate shunt control signal, mediating the relationship between dimming commands and actual current distribution. This intermediary function ensures smooth transitions and uniform brightness by coordinating the shunt switch operation with the PWM signal characteristics.
3Loss of energy
If shunt switch is added in parallel with LED, then energy efficiency is improved, but device complexity increases
Solution Approach 1:
The shunt control circuit performs multiple functions: it receives the PWM dimming signal, generates the shunt control signal with inverted duty cycle, and coordinates the shunt switch operation. By consolidating these functions into a single control circuit, the patent minimizes additional complexity while achieving energy efficiency improvements through the shunt switch mechanism.
Solution Approach 2:
The patent merges the PWM dimming signal processing and shunt switch control into a single shunt control circuit. This integration combines the dimming control function with the shunt control function, reducing the number of separate components and simplifying the overall circuit architecture while maintaining the energy efficiency benefits of the shunt switch.
Data Source
AI summary
A control circuit for a light emitting element driver having a power converter and a shunt switch connected in parallel with the light emitting element. The control circuit has a first control circuit and a second control circuit. The first control circuit provides a dimming process signal and a shunt control signal based on a dimming signal. The second control circuit receives the dimming process signal and a feedback signal representative of an output current of the power converter. When the shunt control signal is at a first level, the shunt switch is turned on, the second control circuit controls the power converter to work in a normal power operation state or a low power operation state. And when the shunt control signal is at a second level, the shunt switch is turned off, the power converter is controlled to work in the normal power operation state.