Dual Switcher Flyback LED Driver Circuit for Flicker Reduction
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Solution Overview
Problem
Solid State Lighting (SSL) devices, such as LED light bulbs, experience visible flicker due to sinusoidal AC mains voltage, which falls below the required minimum voltage, causing the device to switch off at frequencies of 100/120 Hz, resulting in an annoying flicker effect.
Innovation Solution
A driver circuit with a power converter comprising a first and second switcher stage, utilizing a transformer with primary, secondary, and auxiliary windings, and a controller that determines input voltage thresholds to operate the switcher stages accordingly, ensuring a substantially constant output voltage by switching between the input and reservoir capacitor energy sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single switcher stage is used to convert AC mains voltage to constant output voltage, then the device complexity is reduced, but visible flicker occurs when input voltage falls below the minimum threshold
Solution Approach 1:
The power conversion system is divided into two independent switcher stages: a first switcher stage connected to the AC mains voltage input and a second switcher stage connected to a reservoir capacitor. This segmentation allows each stage to operate independently, with the second stage providing continuous power during voltage dips, thereby eliminating flicker while maintaining manageable complexity through modular architecture.
Solution Approach 2:
The controller dynamically changes the operational parameters by switching between two different power sources (AC mains via first switcher stage, or reservoir capacitor via second switcher stage) based on the input voltage level. When input voltage drops below the threshold, the controller transitions to using the second switcher stage, maintaining constant output voltage and eliminating the flicker effect without requiring a completely different system design.
2Power
If the reservoir capacitor is operated at high voltages to handle AC mains variations, then the power conversion capability is improved, but capacitor lifetime and cost are degraded
Solution Approach 1:
Instead of operating the reservoir capacitor at high voltage directly from the AC mains, the system introduces a voltage transformation dimension through the transformer in the first switcher stage. The transformer steps down the high voltage to a lower voltage level, allowing the reservoir capacitor to operate at this reduced voltage while still providing sufficient power through the second switcher stage, thereby extending capacitor lifetime and reducing cost.
Solution Approach 2:
The transformer acts as an intermediary between the high-voltage AC mains and the reservoir capacitor. It transforms the high voltage to a lower voltage level, enabling the capacitor to be operated at reduced voltage stress. This intermediary device allows the system to maintain high power conversion capability from the mains while protecting the capacitor from high voltage damage, improving reliability and reducing cost.
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
The solution effectively reduces or eliminates visible flicker in SSL devices by maintaining a constant output voltage despite significant input voltage variations, using cost-efficient capacitors with extended lifetimes and improved power factor control.
Implementation Method 1
a transformer with primary, secondary, and auxiliary windings
Implementation Method 2
switching between the input and reservoir capacitor energy sources
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
The present document relates to driver circuits which are configured to reduce or remove flicker of SSL devices. A controller (306) for controlling a power converter to convert electrical power at an input voltage (230) into electrical power at an output voltage (231) is described. The power converter comprises a first switcher stage comprising a primary winding (320) of a transformer (307) in series with a first power switch (202) and in parallel to the input voltage (230). The power converter comprises a second switcher stage comprising an auxiliary winding (322) of the transformer (307) in series with a second power switch (503) and in parallel to a reservoir capacitor (501). A secondary winding (321) of the transformer (307) forms an output of the power converter. The controller (306) is configured to determine whether the input voltage (230) is greater or smaller than a pre-determined voltage threshold (403); to operate the first switcher stage during a first time period when the input voltage (230) is greater than the threshold (403); and to operate the second switcher stage during a second time period when the input voltage (230) is smaller than the threshold (403). (Fig. 5)